Toner, process for producing the same, two-component developing agent and method of image formation

ABSTRACT

Toner includes aggregated particles including at least resin particles, pigment particles, and wax particles. A fused film of the resin is formed on the surface of the toner. The wax is at least one selected from A: ester wax that has an iodine value of not more than 25, a saponification value of 30 to 300, and an endothermic peak temperature (melting point) of 50° C. to 100° C. based on a DSC method; and B: wax that is obtained by a reaction of alkyl alcohol having a carbon number of 4 to 30, unsaturated polycarboxylic acid or its anhydride, and unsaturated hydrocarbon wax and has an acid value of 1 to 80 mgKOH/g and an endothermic peak temperature (melted point) of 50° C. to 120° C. based on the DSC method. The toner and a two-component developer can achieve oilless fixing that prevents offset without using oil while maintaining high OHP transmittance, can eliminate spent of the toner components on a carrier to make the life longer, and can ensure high transfer efficiency by suppressing transfer voids or scattering during transfer.

TECHNICAL FIELD

The present invention relates to toner used, e.g., in copiers, laserprinters, plain paper facsimiles, color PPC, color laser printers, colorfacsimiles or multifunctional devices, a method for producing the toner,a two-component developer, and an image forming method.

BACKGROUND ART

In recent years, electrophotographic apparatuses, which commonly wereused in offices, have been used increasingly for personal purposes, andthere is a growing demand for technologies that can achieve, e.g., asmall size, a high speed, high image quality, or high reliability forthose apparatuses. Under such circumstances, a cleanerless process, atandem color process, and oilless fixing are required along with bettermaintainability and less ozone emission. The cleanerless process allowsresidual toner in transfer to be recycled for development withoutcleaning. The tandem color process enables high-speed output of colorimages. The oilless fixing can provide clear color images with highglossiness, transmittance, and offset resistance, even if no fixing oilis used to prevent offset during fixing. These functions should beperformed simultaneously, and therefore improvements in the tonercharacteristics as well as the processes are important factors.

For color printers, a color process employing a four-pass system hasbeen put to practical use. In this color process, an image supportmember (referred to as a photoconductive member in the following) ischarged by corona discharge with a charger, and then is exposed to lightsignals for a latent image of each color to form an electrostatic latentimage. The electrostatic latent image is developed by a first color oftoner, e.g., yellow toner, to form a visible image. Then, a transfermember charged with the opposite polarity to that of the charged yellowtoner comes into contact with the photoconductive member so that theyellow toner image formed on the photoconductive member is transferred.The photoconductive member is cleaned by removing residual toner thathas not been transferred, and the development and transfer of the firstcolor toner ends with discharging the photoconductive member.Subsequently, the same operations as those for the yellow toner arerepeated for toner of colors such as magenta and cyan. The toner imagesof the colors are superimposed on the transfer member so as to form acolor image. Then, the superimposed toner image is transferred to papercharged with the opposite polarity to that of the toner.

A tandem color process employing the following configuration also hasbeen proposed. A plurality of image forming stations, each of whichincludes a charger, a photoconductive member, and a developing unit, arearranged in a row. A first transfer process is performed by successivelytransferring each color of toner to an endless transfer member incontact with the photoconductive members, so that multilayer transfercolor toner images are formed on the transfer member. Then, a secondtransfer process is performed such that the multilayer toner imagesformed on the transfer member are transferred collectively to a transfermedium such as paper, an overhead projector (OHP) sheet, or the like.Another tandem color process also has been proposed in which tonercontinuously is transferred directly to the transfer medium withoutusing the transfer member.

In a fixing process for color images, color toner should be melted andmixed to increase the transmittance. A melt failure of the toner maycause light scattering on the surface or the inside of the toner images,and the original color of the toner pigment is affected. Moreover, lightdoes not reach the lower layer of the superimposed images, resulting inpoor color reproduction. Therefore, it is essential for the toner tohave a complete melt property and transmittance high enough not toreduce the original color. The light transmittance for an OHP sheet alsois a necessary property for the color toner.

When color images are formed, toner may adhere to the surface of afixing roller and cause offset. Therefore, a large amount of oil or thelike should be applied to the fixing roller, which makes the handling orconfiguration of equipment more complicated. Thus, oilless fixing (nooil is used for fixing) is required to provide compact,maintenance-free, and low-cost equipment. To achieve the oilless fixing,e.g., toner in which a release agent (wax) is added to a binder resinwith a sharp melt property is being put to practical use.

However, such toner is very prone to a transfer failure or disturbanceof the toner images during transfer because of its strong cohesiveness.Therefore, it is difficult to ensure compatibility between transfer andfixing. In the case of two-component development, spent (i.e., alow-melting component of the toner adhering to the surface of a carrier)is likely to occur by heat generated by mechanical collision or frictionbetween the particles or between the particles and the developing unit.This decreases the charging ability of the carrier and interferes with alonger life of the developer.

Japanese patent No. 2801507 (Patent Document 1) discloses a carrier forpositively charged toner that is obtained by introducing afluorine-substituted alkyl group into a silicone resin of the coatinglayer. JP 2002-23429 A (Patent Document 2) discloses a coating carrierthat includes conductive carbon and a cross-linked fluorine modifiedsilicone resin. This coating carrier is considered to have highdevelopment ability in a high-speed process and maintain the developmentability for a long time. While taking advantage of superior chargingcharacteristics of the silicone resin, the conventional technique usesthe fluorine-substituted alkyl group to obtain properties such asslidability, releasability, and repellency, to increase resistance towearing, peeling, or cracking, and further to prevent spent. However,the resistance to wearing, peeling, or cracking is not sufficient.Moreover, when the negatively charged toner is used, the amount ofcharge is excessively small, although the positively charged toner mayhave an appropriate amount of charge. Therefore, the reversely chargedtoner (positively charged toner) is generated significantly, which leadsto fog or toner scattering. Thus, the toner is not suitable forpractical use.

Various configurations of toner also have been proposed. It iswell-known that toner for electrostatic charge image development used inan electrophotographic method generally includes a resin component(binder resin), a coloring component including a pigment or dye, aplasticizer, a charge control agent, and an additive, if necessary, suchas a release agent. As the resin component, natural or synthetic resinmay be used alone or in combination.

After the additive is pre-mixed in an appropriate ratio, the mixture isheated and kneaded by thermal melting, pulverized by an air streamcollision board system, and classified as fine powders, thus producing atoner base. In this case, the toner base also may be produced by achemical polymerization method. Then, an additive such as hydrophobicsilica is added to the toner base, so that the toner is completed. Thesingle component development typically uses toner only, and thetwo-component development uses a developer including toner and a carrierof magnetic particles.

Even with pulverization and classification of the conventional kneadingand pulverizing processes, the actual particle size can be reduced toonly about 8 μm in view of the economic and performance conditions. Atpresent, various methods are considered to produce toner having asmaller particle size. In addition, a method for achieving the oillessfixing also is considered, e.g., by adding a release agent (wax) to aresin with a low softening point during melting and kneading. However,there is a limit to the amount of wax to be added, and increasing theamount of wax can cause problems such as low flowability of the toner,transfer voids, or a fusion of the toner to the photoconductive member.

Therefore, various ways of polymerization different from the kneadingand pulverizing processes have been studied as a method for producingtoner. For example, toner may be produced by suspension polymerization.However, the particle size distribution is no better than that of thekneading and pulverizing processes, and in many cases furtherclassification is necessary. Moreover, since the toner is almostspherical in shape, the cleaning property is extremely poor when thetoner remains on the photoconductive member or the like, and thus thereliability of image quality is reduced.

Toner may be produced by emulsion polymerization including the followingsteps: preparing an aggregated particle dispersion by forming aggregatedparticles in a dispersion of at least resin particles; forming adhesiveparticles by mixing a resin particle dispersion in which resin fineparticles are dispersed with the aggregated particle dispersion so thatthe resin fine particles adhere to the aggregated particles; and heatingand fusing the adhesive particles together.

JP 10(1998)-198070 (Patent Document 3) discloses a method for producingtoner for electrostatic charge image development. The method includesthe following steps: preparing a resin particle dispersion by dispersingresin particles in a surface-active agent having a polarity; preparing acoloring agent particle dispersion by dispersing coloring agentparticles in a surface-active agent having a polarity; and preparing aliquid mixture by mixing at least the resin particle dispersion and thecoloring agent particle dispersion. According to this method, thesurface-active agents included in the liquid mixture have the samepolarity, so that reliable toner with excellent charge and colordevelopment properties can be produced in a simple and easy manner.

JP 10(1998)-301332 (Patent Document 4) discloses a method for producingtoner with an excellent fixing property, color development property,transparency, and color mixing property. According to this method, arelease agent includes at least one kind of ester that contains at leastone selected from higher alcohol having a carbon number of 12 to 30 andhigher fatty acid having a carbon number of 12 to 30, and resinparticles include at least two kinds of resin particles with differentmolecular weights.

As the release agent, e.g., low molecular-weight polyolefins such aspolyethylene, polypropylene, and polybutene, silicones, fatty acidamides such as oleamide, erucamide, amide ricinoleate, and amidestearate, vegetable waxes such as carnauba wax, rice wax, candelillawax, Japan wax, and jojoba oil, animal waxes such as beeswax,mineral/petroleum waxes such as montan wax, ozocerite, ceresin, paraffinwax, microcrystalline wax, and Fischer-Tropsch wax, and modified waxesthereof are disclosed.

However, when the dispersibility of the release agent added is lowered,the toner images melted during fixing are prone to a dull color. Thisalso decreases the pigment dispersibility, and thus the colordevelopment property of the toner becomes insufficient. In thesubsequent process, when resin fine particles further adhere to thesurface of an aggregate, the adhesion of the resin fine particles isunstable due to low dispersibility of the release agent or the like.Moreover, the release agent that once was aggregated with the resinparticles is liberated into an aqueous medium. Depending on the polarityor the thermal properties such as a melting point, the release agent mayhave a considerable effect on aggregation. Further, a specified wax isadded in a large amount to achieve the oilless fixing. Therefore, it isdifficult to aggregate the wax with the resin particles that differ fromthe wax in melting point, softening point, and viscoelasticity and tofuse them together uniformly by heating. In particular, the use of arelease agent having a predetermined acid value and a functional groupmay achieve the oilless fixing, reduce fog during development, andimprove the transfer efficiency. However, such a release agent preventsuniform mixing and aggregation of the resin particles with pigmentparticles in an aqueous medium during manufacture. Thus, there is atendency to increase the presence of release agent or pigment suspendedin the aqueous medium.

Patent Document 1: Japanese Patent No. 2801507

Patent Document 2: JP 2002-23429 A

Patent Document 3: JP 10(1998)-198070 A

Patent Document 4: JP 10(1998)-301332 A

DISCLOSURE OF INVENTION

It is an object of the present invention to provide toner, atwo-component developer, and an image forming method that can achieveoilless fixing that prevents offset without using oil while maintaininghigh OHP transmittance, can eliminate spent of the toner components on acarrier to make the service life longer, and can ensure high transferefficiency by suppressing transfer voids or scattering during transfer.

Toner of the present invention includes aggregated particles includingat least resin particles, pigment particles, and wax particles. A fusedfilm of the resin is formed on the surface of the toner. The wax is atleast one selected from A: ester wax that has an iodine value of notmore than 25, a saponification value of 30 to 300, and an endothermicpeak temperature (melting point) of 50° C. to 100° C. based on a DSCmethod, and B: wax that is obtained by the reaction of alkyl alcoholhaving a carbon number of 4 to 30, unsaturated polycarboxylic acid orits anhydride, and unsaturated hydrocarbon wax and has an acid value of1 to 80 mgKOH/g and an endothermic peak temperature (melted point) of50° C. to 120° C. based on the DSC method.

A method for producing toner of the present invention includes thefollowing: forming aggregated particles in an aqueous medium by mixingand aggregating (a) a first resin particle dispersion in which firstresin particles are dispersed in a surface-active agent, (b) a colorantparticle dispersion in which colorant particles are dispersed in asurface-active agent having the same polarity as that of thesurface-active agent for the first resin particle dispersion, (c1) a waxparticle dispersion in which at least ester wax that has an iodine valueof not more than 25, a saponification value of 30 to 300, and anendothermic peak temperature (melting point) of 50° C. to 100° C. basedon a DSC method is dispersed in a surface-active agent having theopposite polarity to that of the surface-active agent for the firstresin particle dispersion, or (c2) a wax particle dispersion in which atleast wax that is obtained by the reaction of alkyl alcohol having acarbon number of 4 to 30, unsaturated polycarboxylic acid or itsanhydride, and unsaturated hydrocarbon wax and has an acid value of 1 to80 mgKOH/g and an endothermic peak temperature (melted point) of 50° C.to 120° C. based on the DSC method is dispersed in a surface-activeagent having the opposite polarity to that of the surface-active agentfor the first resin particle dispersion, and (d) a surface-active agenthaving the same polarity as that of the surface-active agent for the waxparticle dispersion; forming melted particles by heating the aggregatedparticles for a predetermined time in the aqueous medium; mixing themelted particles with a second resin particle dispersion in which secondresin particles are dispersed in a surface-active agent (e) so that thesecond resin particles adhere to the melted particles; and forming fusedfilms of the second resin particles on the surfaces of the meltedparticles by heating.

A two-component developer of the present invention includes toner and acarrier. The toner includes aggregated particles including at leastresin particles, pigment particles, and wax particles. A fused film ofthe resin is formed on the surface of the toner. The wax is at least oneselected from A: ester wax that has an iodine value of not more than 25,a saponification value of 30 to 300, and an endothermic peak temperature(melting point) of 50° C. to 100° C. based on a DSC method, and B: waxthat is obtained by the reaction of alkyl alcohol having a carbon numberof 4 to 30, unsaturated polycarboxylic acid or its anhydride, andunsaturated hydrocarbon wax and has an acid value of 1 to 80 mgKOH/g andan endothermic peak temperature (melted point) of 50° C. to 120° C.based on the DSC method. The carrier includes magnetic particles as acore material, and at least the surface of the core material is coatedwith a fluorine modified silicone resin containing an aminosilanecoupling agent.

A first image forming method of the present invention includes thefollowing: forming electrostatic latent images by using a plurality oftoner image forming stations, each of which includes an image supportmember, a charging member for forming an electrostatic latent image onthe image support member, and a toner support member; making theelectrostatic latent images formed on the image support members visibleby development with toner including aggregated particles that include atleast resin particles, pigment particles, and wax particles, wherein afused film of the resin is formed on the surface of the toner, and thewax is at least one selected from A: ester wax that has an iodine valueof not more than 25, a saponification value of 30 to 300, and anendothermic peak temperature (melting point) of 50° C. to 100° C. basedon a DSC method, and B: wax that is obtained by the reaction of alkylalcohol having a carbon number of 4 to 30, unsaturated polycarboxylicacid or its anhydride, and unsaturated hydrocarbon wax and has an acidvalue of 1 to 80 mgKOH/g and an endothermic peak temperature (meltedpoint) of 50° C. to 120° C. based on the DSC method; and performing atransfer system that includes a primary transfer process and a secondarytransfer process. In the primary transfer process, toner images obtainedby the development of the electrostatic latent images are transferred toan endless transfer member that is in contact with each of the imagesupport members. The primary transfer process is carried outcontinuously in sequence so that a multilayer toner image is formed onthe transfer member. The secondary transfer process is carried out bycollectively transferring the multilayer toner image from the transfermember to a transfer medium. The transfer system satisfies arelationship expressed by d1/v≦0.65 (sec) where d1 (mm) is a distancebetween a first primary transfer position and a second primary transferposition, or between the second primary transfer position and a thirdprimary transfer position, or between the third primary transferposition and a fourth primary transfer position, and v (mm/s) is acircumferential velocity of the image support member.

A second image forming method of the present invention includes thefollowing: forming electrostatic latent images by using a plurality oftoner image forming stations, each of which includes an image supportmember, a charging member for forming an electrostatic latent image onthe image support member, and a toner support member; making theelectrostatic latent images formed on the image support members visibleby development with a two-component developer including toner and acarrier, the toner including aggregated particles that include at leastresin particles, pigment particles, and wax particles, wherein the waxis at least one selected from A: ester wax that has an iodine value ofnot more than 25, a saponification value of 30 to 300, and anendothermic peak temperature (melting point) of 50° C. to 100° C. basedon a DSC method; and B: wax that is obtained by the reaction of alkylalcohol having a carbon number of 4 to 30, unsaturated polycarboxylicacid or its anhydride, and unsaturated hydrocarbon wax and has an acidvalue of 1 to 80 mgKOH/g and an endothermic peak temperature (meltedpoint) of 50° C. to 120° C. based on the DSC method, and the carrierincludes magnetic particles as a core material, and at least the surfaceof the core material is coated with a fluorine modified silicone resincontaining an aminosilane coupling agent; and performing a transfersystem that includes a primary transfer process and a secondary transferprocess. In the primary transfer process, toner images obtained by thedevelopment of the electrostatic latent images are transferred to anendless transfer member that is in contact with each of the imagesupport members. The primary transfer process is carried outcontinuously in sequence so that a multilayer toner image is formed onthe transfer member. The secondary transfer process is carried out bycollectively transferring the multilayer toner image from the transfermember to a transfer medium. The transfer system satisfies arelationship expressed by d1/v≦0.65 (sec) where d1 (mm) is a distancebetween a first primary transfer position and a second primary transferposition, or between the second primary transfer position and a thirdprimary transfer position, or between the third primary transferposition and a fourth primary transfer position, and v (mm/s) is acircumferential velocity of the image support member.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view showing the configuration of an imageforming apparatus used in an example of the present invention.

FIG. 2 is a cross-sectional view showing the configuration of a fixingunit used in an example of the present invention.

FIG. 3 is a schematic perspective view of a wax dispersing device in anembodiment of the present invention.

FIG. 4 is a plan view of the wax dispersing device in FIG. 3.

FIG. 5 is a schematic process chart showing a production method of

FIG. 6A is a transmission electron microscope (TEM) image of tonerparticles of a toner base produced in an example of the presentinvention (magnification: 15000×).

FIG. 6B is a TEM image of toner particles of a toner base produced inanother example of the present invention (magnification: 12000×).

1: photoconductive member, 2: charging roller, 3: laser signal light, 4:developing roller, 5: blade, 10: first transfer roller, 12: transferbelt, 14: second transfer roller, 13: driving tension roller, 17:transfer belt unit 18K, 18C, 18M, 18Y: image forming units, 18: imageforming unit group, 20: emulsion polymerization tank, 30: pigmentdispersion tank, 40: wax dispersion tank, 50: aggregation tank, 60:filtration separation tank, 70: washing tank, 201: fixing roller, 202:pressure roller, 203: fixing belt, 205: induction heater, 206: ferritecore, 207: coil

DESCRIPTION OF THE INVENTION

The present invention provides toner for electrostatic charge imagedevelopment that has a smaller particle size and a sharp particle sizedistribution and that can exhibit high charging characteristics,environmental dependence, cleaning property, and transfer property, anda two-component developer. The present invention also provides an imageforming method that can form color images with high quality andreliability without causing toner scattering, fog, or the like.

(1) Wax

The toner of the present invention includes wax. The wax is required notonly to improve the anti-offset property of the toner in fixing, butalso to satisfy the electrophotographic characteristics, e.g., bypreventing fog or scattering during development as well as reversetransfer or transfer voids. In view of this, the present inventorsstudied various kinds of wax. For low molecular weight polyolefin wax ofpolyethylene or polypropylene, it was difficult to disperse the waxfinely in the liquid to form a dispersion, and the amount of waxliberated became larger in an aggregation reaction. When the wax wasused in color toner, it was difficult to produce a clear color imagebecause the image was prone to a dull color. For fatty acid amide wax ofoleic acid amide, erucic acid amide, or stearic acid amide, the wax wasdispersed finely in the liquid to form a dispersion. However,reaggregation of the wax was likely to occur over time, and thushandling was a problem. For paraffin wax, microcrystalline wax, andFischer-Tropsch wax, it was difficult to disperse the wax in the liquidto form a dispersion, and the amount of wax liberated became larger inan aggregation reaction.

As a result of the above study, the present inventors found wax that canbe dispersed finely in the liquid to form a dispersion, causes noreaggregation over time, and is not liberated during an aggregationreaction. The present inventors also focused on the characteristics ofthe wax that do not impair the fixing, development, and transferproperties.

The wax added to the toner of the present invention preferably has aniodine value of not more than 25 and a saponification value of 30 to300. The amount of wax added is preferably 1 to 20 parts by weight per100 parts by weight of the binder resin. This wax can relieve therepulsion caused by the charging action of the toner during multilayertransfer and also can suppress a reduction in transfer efficiency,transfer voids, or reverse transfer. By combining the wax with acarrier, it is possible to suppress the occurrence of spent on thecarrier. Accordingly, the life of a developer can be made longer.Further, the handling property of the toner in a developing unit can beimproved, so that the image uniformity can be improved in both the startand end of the development. The generation of a developing memory alsocan be reduced. The wax can be mixed and aggregated uniformly with theresin particles and the pigment particles by a surface-active agenthaving a specific polarity, which will be described later. This caneliminate the suspended solids, thereby suppressing a dull color. In thesubsequent process, the wax is not liberated easily while a resin isfused further.

The amount of wax added is preferably 5 to 20 parts by weight, and morepreferably 10 to 20 parts by weight per 100 parts by weight of thebinder resin. When it is less than 5 parts by weight, the effect ofimproving the fixability cannot be obtained. When it is more than 20parts by weight, the storage stability is a problem.

When the iodine value of the wax is more than 25, the mixing andaggregation of the wax in the aqueous medium become poor, and uniformdispersibility is decreased to cause a dull color. Moreover, suspendedsolids are increased and remain in the toner, which may lead to filmingof the toner on a photoconductive member or the like. This makes itdifficult to relieve the repulsion caused by the charging action of thetoner during multilayer transfer in the primary transfer process. Theenvironmental dependence is large, and a change in chargeability of thematerial is increased to impair the image stability over a long periodof continuous use. Further, a developing memory can be generated easily.

When the saponification value of the wax is less than 30, the presenceof unsaponifiable matter and hydrocarbon is increased, resulting infilming of the toner on a photoconductive member or low chargeability.Moreover, the dispersibility of the wax with a charge control agent isdecreased to cause filming or low chargeability of the toner duringcontinuous use. When the saponification value is more than 300, thedispersibility of the wax with a resin is decreased, thus making itdifficult to relieve the repulsion caused by the charging action of thetoner during multilayer transfer. Moreover, fog or toner scattering maybe increased.

The binder resin preferably has an acid value of 1 to 40 mgKOH/g. Whenthe acid value is less than 1 mgKOH/g, it is difficult to relieve therepulsion caused by the charging action of the toner during multilayertransfer. When the acid value is more than 40 mgKOH/g, the environmentalresistance is reduced to increase fog.

The melting point of the wax based on a DSC method is preferably 50° C.to 100° C. More preferably, the wax may have an iodine value of not morethan 15, a saponification value of 50 to 250, and a melting point of 65°C. to 90° C. based on the DSC method. Further preferably, the wax mayhave an iodine value of not more than 5, a saponification value of 70 to200, and a melting point of 65° C. to 85° C. based on the DSC method.

A preferred material for the wax may have a rate of volume increase of 2to 30% when the temperature changes by 10° C. above the melting point.The wax expands rapidly upon changing from solid to liquid, so that whenit is melted by heat during fixing, the toner particles adhere to eachother more strongly. This further can improve the fixability, thereleasing property for the fixing roller, and the offset resistance.When the rate of volume increase is smaller than 2%, these effects arereduced. When it is larger than 30%, the dispersibility is likely to bedecreased during kneading.

The wax preferably has a heating loss of not more than 8 wt % at 220° C.When the heating loss is more than 8 wt %, the glass transition point ofthe toner becomes low, and the storage stability is degraded. Therefore,such wax adversely affects the development property and allows fog orfilming of the toner on a photoconductive member to occur.

Among the molecular weight characteristics of the wax based on gelpermeation chromatography (GPC), it is preferable that thenumber-average molecular weight is 100 to 5000, the weight-averagemolecular weight is 200 to 10000, the ratio (weight-average molecularweight/number-average molecular weight) of the weight-average molecularweight to the number-average molecular weight is 1.01 to 8, the ratio (Zaverage molecular weight/number-average molecular weight) of the Zaverage molecular weight to the number-average molecular weight is 1.02to 10, and there is at least one molecular weight maximum peak in therange of 5×10² to 1×10⁴. It is more preferable that the number-averagemolecular weight is 500 to 4500, the weight-average molecular weight is600 to 9000, the weight-average molecular weight/number-averagemolecular weight ratio is 1.01 to 7, and the Z average molecularweight/number-average molecular weight ratio is 1.02 to 9. It is furtherpreferable that the number-average molecular weight is 700 to 4000, theweight-average molecular weight is 800 to 8000, the weight-averagemolecular weight/number-average molecular weight ratio is 1.01 to 6, andthe Z average molecular weight/number-average molecular weight ratio is1.02 to 8.

When the number-average molecular weight is less than 100, theweight-average molecular weight is less than 200, and the molecularweight maximum peak is smaller than 5×10², the storage stability islikely to be degraded. Moreover, the handling property of the toner in adeveloping unit is reduced to impair the uniformity of the tonerconcentration. Further, the filming of the toner on a photoconductivemember may occur.

When the number-average molecular weight is more than 5000, theweight-average molecular weight is more than 10000, the weight-averagemolecular weight/number-average molecular weight ratio is more than 8,the Z average molecular weight/number-average molecular weight ratio ismore than 10, and the molecular weight maximum peak is in the rangelarger than 1×10⁴, the releasing action is weakened, and the fixingfunctions such as fixability and offset resistance are likely to bedegraded.

Preferred materials for the wax may be, e.g., meadowfoam oil, jojobaoil, Japan wax, beeswax, ozocerite, carnauba wax, candelilla wax,ceresin wax, rice wax, and derivatives thereof They can be usedindividually or in combinations of two or more. In particular, at leastone selected from carnauba wax with a melting point of 76° C. to 90° C.,candelilla wax with a melting point of 66° C. to 80° C., hydrogenatedjojoba oil with a melting point of 64° C. to 78° C., hydrogenatedmeadowfoam oil with a melting point of 64° C. to 78° C., and rice waxwith a melting point of 74° C. to 90° C. base on the DSC method also canbe used preferably.

The saponification value is the milligrams of potassium hydroxide (KOH).required to saponify 1 g sample and corresponds to the sum of an acidvalue and an ester value. When the saponification value is measured, asample is saponified with approximately 0.5N potassium hydroxide in analcohol solution, and then excess potassium hydroxide is titrated with0.5N hydrochloric acid.

The iodine value may be determined in the following manner. The amountof halogen absorbed by a sample is measured while the halogen acts onthe sample. Then, the amount of halogen absorbed is converted to iodineand expressed in grams per 100 g of the sample. The iodine value isgrams of iodine absorbed by 100 g fat, and the degree of unsaturation offatty acid in the sample increases with the iodine value. A chloroformor carbon tetrachloride solution is prepared as a sample, and an alcoholsolution of iodine and mercuric chloride or a glacial acetic acidsolution of iodine chloride is added to the sample. After the sample isallowed to stand, the iodine that remains without causing any reactionis titrated with a sodium thiosulfate standard solution, thuscalculating the amount of iodine absorbed.

The heating loss may be measured in the following manner. A sample cellis weighed precisely to the first decimal place (W1 mg). Then, 10 to 15mg of sample is placed in the sample cell and weighed precisely to thefirst decimal place (W2 mg). This sample cell is set in a differentialthermal balance and measured with a weighing sensitivity of 5 mg. Aftermeasurement, the weight loss (W3 mg) of the sample at 220° C. is read tothe first decimal place using a chart. The measuring device is, e.g.,TGD-3000 (manufactured by ULVAC-RICO, Inc.), the rate of temperaturerise is 10° C./min, the maximum temperature is 220° C., and theretention time is 1 min. Accordingly, the heating loss (%) can bedetermined by W3/(W2−W1)×100. Thus, the transmittance in color imagesand the offset resistance can be improved. Moreover, it is possible tosuppress the occurrence of spent on a carrier and to increase the lifeof a developer.

The following wax also can be used preferably: wax obtained by thereaction of alkyl alcohol having a carbon number of 4 to 30, unsaturatedpolycarboxylic acid or its anhydride, and unsaturated hydrocarbon wax;wax obtained by the reaction of alkylamine, unsaturated polycarboxylicacid or its anhydride, and unsaturated hydrocarbon wax; or wax obtainedby the reaction of fluoroalkyl alcohol, unsaturated polycarboxylic acidor its anhydride, and unsaturated hydrocarbon wax.

For the molecular weight distribution of this wax based on GPC, it ispreferable that the weight-average molecular weight is 1000 to 6000, theZ average molecular weight is 1500 to 9000, the ratio (weight-averagemolecular weight/number-average molecular weight) of the weight-averagemolecular weight to the number-average molecular weight is 1.1 to 3.8,the ratio (Z average molecular weight/number-average molecular weight)of the Z average molecular weight to the number-average molecular weightis 1.5 to 6.5, there is at least one molecular weight maximum peak inthe range of 1×10³ to 3×10⁴, the acid value is 1 to 80 mgKOH/g, themelting point is 50° C. to 120° C., and the penetration number is notmore than 4 at 25° C. It is more preferable that the weight-averagemolecular weight is 1000 to 5000, the Z average molecular weight is 1700to 8000, the weight-average molecular weight/number-average molecularweight ratio is 1.1 to 2.8, the Z average molecularweight/number-average molecular weight ratio is 1.5 to 4.5, there is atleast one molecular weight maximum peak in the range of 1×10³ to 1×10⁴,the acid value is 10 to 70 mgKOH/g, and the melting point is 60° C. to110° C. It is further preferable that the weight-average molecularweight is 1000 to 2500, the Z average molecular weight is 1900 to 3000,the weight-average molecular weight/number-average molecular weightratio is 1.2 to 1.8, the Z average molecular weight/number-averagemolecular weight ratio is 1.7 to 2.5, there is at least one molecularweight maximum peak in the range of 1×10³ to 3×10³, the acid value is 35to 50 mgKOH/g, and the melting point is 65° C. to 95° C. The wax withthe above molecular weight distributions can contribute to higher offsetresistance, glossiness, and OHP transmittance in the oilless fixing.Moreover, the wax does not decrease the storage stability at hightemperatures. When an image is formed by arranging three layers of colortoner on a thin paper, the wax is particularly effective to improve theseparatability of the paper from the fixing roller or belt. The wax canbe mixed and aggregated uniformly with the resin particles and thepigment particles. This can eliminate the suspended solids, therebysuppressing a dull color. When a resin further is fused with theparticles, the liberation of the wax is not likely to occur, and themixing and dispersing state can be produced easily. Even if a fluorineor silicone material is used for the fixing roller, offset of a halftoneimage can be suppressed.

By combining the wax with a carrier, which will be described later, itis possible not only to achieve the oilless fixing but also to suppressthe occurrence of spent on the carrier. Accordingly, the service life ofa developer can be made longer. While the uniformity of the toner in adeveloping unit can be maintained, the generation of a developing memoryalso can be reduced. Further, the charge stability can be maintainedduring continuous use, which ensures compatibility between thefixability and the development stability.

When the carbon number of the alkyl group of the wax is less than 4, thereleasing action is weakened, so that the separatability and thehigh-temperature offset resistance are degraded. When the carbon numberis more than 30, the mixing and aggregation of the wax with the resinparticles become poor, resulting in low dispersibility. When the acidvalue is less than 1 mgKOH/g, the amount of charge of the toner isreduced over a long period of use. When the acid value is more than 80mgKOH/g, the moisture resistance is decreased to increase fog under highhumidity.

When the melting point is less than 50° C., the storage stability of thetoner is degraded. When it is more than 120° C., the releasing action isweakened, and the temperature range of offset resistance is narrowed.Moreover, it is difficult to reduce the particle size of the emulsifiedand dispersed particles of the wax.

When the penetration number is more than 4 at 25° C., the toughness isreduced to cause filming of the toner on a photoconductive member over along period of use.

When the weight-average molecular weight is less than 1000, the Zaverage molecular weight is less than 1500, the weight-average molecularweight/number-average molecular weight ratio is less than 1.1, the Zaverage molecular weight/number-average molecular weight ratio is lessthan 1.5, and the molecular weight maximum peak is in the range smallerthan 1×10³, the storage stability of the toner is degraded, thus causingfilming of the toner on a photoconductive member or intermediatetransfer member. Moreover, the handling property of the toner in adeveloping unit is reduced to impair the uniformity of the tonerconcentration. Further, a developing memory can be generated easily.Thus, when emulsified and dispersed particles are produced under thestrong shearing force of a high-speed rotating body, the particle sizedistribution becomes broader.

When the weight-average molecular weight is more than 6000, the Zaverage molecular weight is more than 9000, the weight-average molecularweight/number-average molecular weight ratio is more than 3.8, the Zaverage molecular weight/number-average molecular weight ratio is morethan 6.5, and the molecular weight maximum peak is in the range largerthan 3×10⁴, the releasing action is weakened, and the fixing functionsare degraded. Moreover, it is difficult to reduce the particle size ofthe emulsified and dispersed particles of the wax, and the mixing anddispersing state cannot be produced easily.

Examples of the alcohol include alcohols having an alkyl chain with acarbon number of 4 to 30 such as octanol (C₈H₁₇OH), dodecanol(C₁₂H₂₅OH), stearyl alcohol (C₁₈H₃₇OH), nonacosanol (C₂₉H₅₉OH), andpentadecanol (C₁₅H₃₁OH). Examples of the amines includeN-methylhexylamine, nonylamine, stearylamine, and nonadecylamine.Examples of the fluoroalkyl alcohol include1-methoxy-(perfluoro-2-methyl-1-propene), hexafluoroacetone,3-perfluorooctyl-1, and 2-epoxypropane. Examples of the unsaturatedpolycarboxylic acid or its anhydride include maleic acid, maleicanhydride, itaconic acid, itaconic anhydride, citraconic acid, andcitraconic anhydride. They can be used individually or in combinationsof two or more. In particular, the maleic acid and the maleic anhydrideare preferred. Examples of the unsaturated hydrocarbon wax includeethylene, propylene, and α-olefin.

The unsaturated polycarboxylic acid or its anhydride is polymerizedusing alcohol or amine, and then is added to a synthetic hydrocarbon waxin the presence of dicumyl peroxide or tert-butylperoxy isopropylmonocarbonate.

The amount of wax added is preferably 1 to 20 parts by weight per 100parts by weight of the binder resin. When it is less than 1 part byweight, the releasing effect cannot be obtained easily. When it is morethan 20 parts by weight, the flowability of the toner is decreased, andthe effect is no longer improved due to saturation.

A wax particle dispersion is prepared by heating and melting wax indistilled water, adding a surface-active agent having a polarity to thewax melt, and dispersing the wax with a dispersing means. When the waxhas a high melting point, it may be melted by heating under highpressure so as to form a dispersion.

The above wax has a specific polar group. Therefore, it is preferablethat lauryl amine hydrochloride or stearic acid amine hydrochloride isused as a cationic surface-active agent. This allows the dispersion tobe finer. Moreover, when the aggregated particles are formed by anaggregation reaction, less wax is liberated, so that a uniform narrowparticle size distribution can be achieved. In such a case,water-soluble polymer components such as polyvinyl alcohol orwater-soluble cellulose may be added simultaneously with the laurylamine hydrochloride or stearic acid amine hydrochloride, therebyimproving the dispersion stability.

As the dispersing means, e.g., a homogenizer can be used to produce adispersion with a median diameter of 0.2 to 0.3 μm. However, a finerdispersion with a median diameter of not more than 0.2 μm can beobtained in such a manner that the wax melt is emulsified and dispersedby utilizing the effect of a strong shearing force generated when arotating body rotates at high speed relative to a fixed body with apredetermined gap (about 0.1 mm to 10 mm) between them. The rotatingbody rotates at a high speed of not less than 30 m/s, and preferably notless than 40 m/s and exerts a strong shearing force on the liquid, thusproducing an emulsified dispersion with a finer particle size. A30-second to 5-minute treatment may be enough to obtain the finedispersion.

FIG. 3 is a schematic perspective view of a stirring/dispersing device40 for wax in an embodiment of the present invention. FIG. 4 is a planview of the stirring/dispersing device 40. This device is water coolingjacket type. The whole device is cooled by introducing cooling waterfrom a line 47 to the inside of an outer tank 41 and discharging itthrough a line 48. Reference numeral 42 is a shielding board that stopsthe liquid to be treated flowing. The shielding board 42 has an openingin the central portion, and the treated liquid is drawn from the openingand taken out of the device through a line 45. Reference numeral 43 is arotating body that is secured to a shaft 46 and rotates at high speed.There are holes (about 1 to 5 mm in size) in the side of the rotatingbody 43, and the liquid to be treated can move through the holes. Theliquid to be treated is put into the tank in an amount of about one-halfthe capacity (120 ml) of the tank. The maximum rotational speed of therotating body can be 50 m/s. The rotating body has a diameter of 52 mm,and the tank has an internal diameter of 56 mm. Reference numeral 44 isa material inlet used for a continuous treatment. In the case of ahigh-pressure treatment or batch treatment, the material inlet 44 isclosed.

(2) Resin

As the resin particles of the toner of this embodiment, e.g., athermoplastic binder resin can be used. Specific examples of thethermoplastic binder resin include the following: styrenes such asstyrene, parachloro styrene, and α-methyl styrene; acrylic monomers suchas methyl acrylate, ethyl acrylate, n-propyl acrylate, lauryl acrylate,and 2-ethylhexyl acrylate; methacrylic monomers such as methylmethacrylate, ethyl methacrylate, n-propyl methacrylate, laurylmethacrylate, and 2-ethylhexyl methacrylate; ethylene-unsaturated acidmonomers such as acrylic acid, methacrylic acid, and sodiumstyrenesulfonate; vinyl nitrites such as acrylonitrile andmethacrylonitrile; vinyl ethers such as vinyl methylether and vinylisobutylether; vinyl ketones such as vinyl methylketone, vinylethylketone, and vinyl isopropenylketone; and olefins such as ethylene,propylene, and butadiene, and a homopolymer, a copolymer, or a mixtureof these substances (monomers). The specific examples further mayinclude a non-vinyl condensed resin such an epoxy resin, a polyesterresin, a polyurethane resin, a polyamide resin, a cellulose resin, or apolyether resin, a mixture of the non-vinyl condensed resin and any ofthe vinyl resins as described above, and a graft copolymer formed bypolymerization of vinyl monomers in the presence of the non-vinylcondensed resin.

Among these resins, the vinyl resin is preferred particularly. The vinylresin is advantageous in that a resin particle dispersion can beprepared easily, e.g., by emulsion polymerization or seed polymerizationusing an ionic surface-active agent. Examples of the vinyl monomerinclude a monomer to be used as a material for a vinyl polymer acid or avinyl polymer base, such as acrylic acid, methacrylic acid, maleic acid,cinnamic acid, fumaric acid, vinyl sulfonic acid, ethylene imine, vinylpyridine, or vinyl amine. In the present invention, the resin particlespreferably contain the vinyl monomer as a monomer component. In thepresent invention, the vinyl polymer acid is more preferred among thevinyl monomers in view of ease of the vinyl resin formation reaction.Specifically, a dissociating vinyl monomer having a carboxyl group as adissociation group such as acrylic acid, methacrylic acid, maleic acid,cinnamic acid, or fumaric acid is preferred particularly in terms ofcontrolling the polymerization degree or the glass transition point.

The median diameter of the resin particles is generally not more than 1μm, and preferably 0.01 to 1 μm. When the median diameter is more than 1μm, toner for electrostatic charge image development to be obtained as afinal product can have a broader particle size distribution. Moreover,liberated particles are generated and tend to reduce the performance orreliability. When the median diameter is within the above range, thesedisadvantages are eliminated, and the uneven distribution of toner isdecreased. Therefore, the dispersion of the resin particles in the tonercan be improved, resulting in a smaller variation in performance andreliability. The median diameter can be measured, e.g., by a laserdiffraction particle size analyzer (LA 920 manufactured by Horiba,Ltd.).

The content of resin particles in the resin particle dispersion isgenerally 5 to 60 wt %, and preferably 10 to 40 wt %. When theaggregated particles are formed, the content of resin particles in theaggregated particle dispersion may be not more than 50 wt %, andpreferably about 2 to 40 wt %.

The molecular weights of the resin, wax, and toner can be measured bygel permeation chromatography (GPC) using several types of monodispersepolystyrene as a standard sample. The measurement may be performed withHPLC 8120 series manufactured by TOSOH CORP., using TSK gel super HM-HH4000/H3000/H2000 (7.8 mm diameter, 150 mm×3) as a column and THF(tetrahydrofuran) as an eluent, at a flow rate of 0.6 ml/min, a sampleconcentration of 0.1%, an injection amount of 20 μL, RI as a detector,and at a temperature of 40° C. Prior to the measurement, the sample isdissolved in THF, and then is filtered through a 0.45 μm filter so thatadditives such as silica are removed to measure the resin component. Themeasurement requirement is that the molecular weight distribution of thesubject sample is in the range where the logarithms and the countnumbers of the molecular weights in the analytical curve obtained fromthe several types of monodisperse polystyrene standard samples form astraight line.

The wax obtained by the reaction of alkyl alcohol having a carbon numberof 4 to 30, unsaturated polycarboxylic acid or its anhydride, andunsaturated hydrocarbon wax can be measured with GPC-150C (manufacturedby Waters Corporation), using Shodex HT-806M (8.0 mm I.D.−30 cm×2) as acolumn and o-dichlorobenzene as an eluent, at a flow rate of 1.0 mL/min,a sample concentration of 0.3%, an injection amount of 200 μL, RI as adetector, and at a temperature of 130° C. Prior to the measurement, thesample is dissolved in a solvent, and then is filtered through a 0.5 μmsintered metal filter. The measurement requirement is that the molecularweight distribution of the subject sample is in the range where thelogarithms and the count numbers of the molecular weights in theanalytical curve obtained from the several types of monodispersepolystyrene standard samples form a straight line.

The softening point of the binder resin can be measured with a capillaryrheometer flow tester (CFT-500, constant-pressure extrusion system,manufactured by Shimadzu Corporation). A load of about 9.8×10⁵ N/m² isapplied to a 1 cm³ sample with a plunger while heating the sample at atemperature increase rate of 6° C./min, so that the sample is extrudedfrom a die having a diameter of 1 mm and a length of 1 mm. Based on therelationship between the piston stroke of the plunger and thetemperature increase characteristics, when the temperature at which thepiston stroke starts to rise is a flow start temperature (Tfb), one-halfthe difference between the minimum value of a curve and the flow endpoint is determined. Then, the resultant value and the minimum value ofthe curve are added to define a point, and the temperature of this pointis identified as a melting point (softening point Tm) according to a ½method.

The glass transition point of the resin can be measured with adifferential scanning calorimeter. The temperature of a sample is raisedto 100° C., retained for 3 minutes, and reduced to room temperature at10° C./min. Subsequently, the temperature is raised at 10° C./min, and athermal history of the sample is measured. In the thermal history, anintersection point of an extension line of the base line lower than aglass transition point and a tangent that shows the maximum inclinationbetween the rising point and the highest point of a peak is determined.The temperature of this intersection point is identified as a glasstransition point.

The melting point at an endothermic peak based on the DSC method can bemeasured with a differential scanning calorimeter (DSC-50 manufacturedby Shimadzu Corporation). The temperature of a sample is raised to 200°C. at 5° C./min, retained for 5 minutes, and reduced to 10° C. rapidly.Subsequently, the sample is allowed to stand for 15 minutes, and thetemperature is raised at 5° C./min. Then, the melting point isdetermined from the endothermic (melt) peak. The amount of the sampleplaced in a cell is 10 mg±2 mg.

(3) Polymerization Process

A resin particle dispersion is prepared by forming resin particles of ahomopolymer or copolymer (vinyl resin) of vinyl monomers by emulsion orseed polymerization of the vinyl monomers in an ionic surface-activeagent and dispersing the resin particles in the ionic surface-activeagent. Any known dispersing devices such as a rotating and shearinghomogenizer, a ball mill using a medium, a sand mill, and a Dyno millcan be used. When the resin particles are made of resin other than thehomopolymer or copolymer of the vinyl monomers, a resin particledispersion may be prepared in the following manner. If the resindissolves in an oil solvent that has relatively low water solubility, asolution is obtained by mixing the resin with the oil solvent. Thesolution is blended with an ionic surface-active agent orpolyelectrolyte, and then is dispersed in water to produce a fineparticle dispersion by using a dispersing device such as a homogenizer.Subsequently, the oil solvent is evaporated by heating or under reducedpressure. Thus, the resin particles made of resin other than the vinylresin are dispersed in the ionic surface-active agent. As apolymerization initiator, e.g., an azo- or diazo-based initiator such as2,2′-azobis-(2,4-dimethylvaleronitrile), 2,2′-azobisisobutyronitrile,1,1′-azobis(cyclohexane-1-carbonitrile),2,2′-azobis-4-methoxy-2,4-dimethylvaleronitrile, orazobisisobutyronitrile can be used.

A colorant particle dispersion is prepared by dispersing colorantparticles in an ionic surface-active agent using a dispersing devicesuch as a homogenizer.

A wax particle dispersion can be produced by the method as describedabove. The wax particle dispersion also can be produced in the followingmanner. The wax is dissolved in an oil solvent. This solution is blendedwith an ionic surface-active agent or polyelectrolyte, and then isdispersed in water to produce a fine particle dispersion by using adispersing device such as a homogenizer. Subsequently, the oil solventis evaporated by heating or under reduced pressure.

The colorant particle dispersion may be prepared by dispersing thecolorant particles in a surface-active agent having a polarity using theabove dispersing device.

The wax particle dispersion may be prepared by heating and melting thewax in distilled water, adding a surface-active agent having a polarityto the wax melt, and dispersing the wax with the above dispersingdevice. When the wax has a high melting point, it may be melted byheating under high pressure so as to form a dispersion. Alternatively,the wax is dissolved in an oil solvent. This solution is blended with anionic surface-active agent or polyelectrolyte, and then is dispersed inwater to produce a fine particle dispersion by using the dispersingdevice such as a homogenizer. Subsequently, the oil solvent isevaporated by heating or under reduced pressure.

In a process of mixing and aggregating these dispersions, aggregatedparticles including the first resin particles, the colorant particles,and the wax particles are formed in water. In this case, the polarity ofa surface-active agent contained in the first resin particle dispersionis the same as that of a surface-active agent contained in the colorantparticle dispersion. The polarity of a surface-active agent contained inthe wax particle dispersion is opposite to that of a surface-activeagent used for the resin and the colorant.

Moreover, a surface-active agent having the opposite polarity to that ofa surface-active agent used for the resin and the colorant further isadded separately. This allows the wax having a polarity such as an acidvalue, an alkyl group, or an iodine value to be mixed and aggregateduniformly with the resin and the colorant that have a polar group with apredetermined acid value. Therefore, it is possible to reduce the amountof wax or colorant that is not aggregated and thus is suspended in theaqueous medium, and to form aggregated particles having a sharp particlesize. The mixing can be performed by using any known devices such as ahomogenizer and a mixer.

Thereafter, the aggregated particles are heated for a predetermined timewhile mixing and stirring in the aqueous medium to form meltedparticles. The heating temperature preferably is not less than a glasstransition point of the resin and is less than a temperature 20° C.higher than the glass transition point.

In the above process of mixing and aggregating the dispersions,aggregation may be caused by the addition of an aggregating agent or pHadjustment. However, when the specific wax is used, the particles arenot aggregated stably and are likely to remain suspended in the aqueousmedium.

When the melted particles are formed by heating the aggregated particlesfor a predetermined time in the aqueous medium, a second resin furtheradheres to the melted particles and serves as a coating. In this case,an inorganic salt may be added and fused to make the coating uniform.

The melted particles are controlled to have a volume average particlesize that is about the same as or slightly smaller than the volumeaverage particle size of toner to be obtained as a final product. Theparticles size can be set or changed depending on the amount ofsurface-active agent added, agitating speed, treatment, or temperature.Moreover, the toner can be varied from irregular to spherical in shape.The toner shape becomes closer to a sphere by heating at hightemperatures for a long time.

It is preferable that the dispersion average particle size of the waxparticles is 0.05 to 0.3 μm, the particles of not more than 0.2 μm are65% by number or more, and the particles of more than 0.5 μm are 10% bynumber or less.

When the dispersion average particle size is smaller than 0.05 μm, theload is increased during dispersion, resulting in low productivity. Whenthe particles of more than 0.5 μm are larger than 10% by number, and theparticles of less than 0.2 μm are smaller than 65% by number, uniformdispersion cannot be achieved during mixing and aggregation, and morewax is liberated while the second resin is fused with the meltedparticles. Thus, the toner may increase filming on a photoconductivemember or spent on a carrier and decrease the handling property indevelopment. Moreover, a developing memory may be generated.

A second resin particle dispersion in which the second resin particlesare dispersed is mixed with the melted particle dispersion so that thesecond resin particles adhere to the melted particles. Thesurface-active agent of the second resin particle dispersion has thesame polarity as that of the first resin particle dispersion used informing the aggregated particles. In this case, an inorganic metal saltis added as an aggregating agent to accelerate the adhesion of thesecond resin particles, and thus the production rate can be increased.The pH is adjusted preferably in the range of 7 to 10. The second resinparticles can be fused with the melted particles without causingsecondary aggregation of the melted particles.

Examples of the inorganic metal salt include polyaluminium hydroxide,magnesium sulfate, magnesium chloride, zinc sulfate, ferric chloride,aluminium chloride, and polyaluminium chloride. Among these, thepolyvalent metal salts are preferred. In particular, the aluminiumcompounds are preferred. They can be used individually or incombinations of two or more. The addition of the inorganic metal saltcan suppress the generation of very small particles and ensure a sharpparticle size distribution of the toner to be produced.

It is preferable that when the second resin particles adhere to themelted particles, the temperature of the aqueous medium is not more thana glass transition point of the first resin particles included in themelted particles, and the particles are treated for 30 minutes to 2hours while stirring gently with a mixer or the like. This canfacilitate the adhesion between the melted particles and the secondresin particles, so that the resultant particles are stabilized easily.

After the second resin particles adhere to the melted particles, heatingis performed for 30 minutes to 3 hours at temperatures ranging from aglass transition point of the second resin particles that have adheredto the melted particles in the aqueous medium to the glass transitionpoint +40° C. Consequently, the second resin particles are fused withthe melted particles to form fused films firmly on the surfaces of themelted particles. By covering the surfaces of the melted particles withthe second resin particles, it is possible to prevent the colorant orwax from being exposed on the toner surface. Thus, a charge failure ornonuniform charge due to the exposure can be suppressed effectively.

Thereafter, cleaning, liquid-solid separation, and drying processes maybe performed as desired to provide toner. The cleaning processpreferably involves sufficient substitution cleaning with ion-exchangedwater to improve the chargeability. The liquid-solid separation processis not particularly limited, and any known filtration methods such assuction filtration and pressure filtration can be used preferably inview of productivity. The drying process is not particularly limited,and any known drying methods such as flash-jet drying, flow drying, andvibration-type flow drying can be used preferably in view ofproductivity.

As the surface-active agent having a polarity, e.g., an aqueous mediumincluding a polar surface-active agent may be used. Examples of theaqueous medium include water such as distilled water or ion-exchangedwater, and alcohols. They can be used individually or in combinations oftwo or more. The content of the polar surface-active agent in thesurface-active agent having a polarity cannot be defined generally andmay be selected appropriately depending on the purposes.

As the polar surface-active agent, e.g., a sulfate-based,sulfonate-based, phosphate-based, or soap-based anionic surface-activeagent or an amine salt-type or quaternary ammonium salt-type cationicsurface-active agent may be used.

Specific examples of the anionic surface-active agent include sodiumdodecyl benzene sulfonate, sodium dodecyl sulfate, sodium alkylnaphthalene sulfonate, and sodium dialkyl sulfosuccinate. Specificexamples of the cationic surface-active agent include alkyl benzenedimethyl ammonium chloride, alkyl trimethyl ammonium chloride, anddistearyl ammonium chloride. They can be used individually or incombinations of two or more.

In the present invention, these polar surface-active agents can be usedtogether with a nonpolar surface-active agent. As the nonpolarsurface-active agent, e.g., a polyethylene glycol-based, alkylphenolethylene oxide adduct-based, or polyhydric alcohol-based nonionicsurface-active agent may be used.

(4) Charge Control Agent

As the charge control agent, e.g., particles of a triphenylmethane dyeor dye including a complex of quarternary ammonium salt compound,nigrosine compound, aluminum, iron, or chromium can be used. The chargecontrol agent also may be an acrylic/sulfonic acid polymer, andpreferably a vinyl copolymer of a styrene monomer and an acrylic acidmonomer having a sulfonic group as a polar group. In particular, anacrylamide-2-methylpropane sulfonic acid copolymer can provide favorablecharacteristics. By combining the charge control agent with the carrier,the handling property of the toner in a developing unit can be improved,thus increasing the uniformity of the toner concentration. Moreover, thegeneration of a developing memory can be reduced.

Preferred materials for the charge control agent may include a metalsalt of a salicylic acid derivative expressed by Formula (1) and a metalsalt of a benzilic acid derivative expressed by Formula (2).

(where R¹ and R⁴ independently represent a hydrogen atom, astraight-chain or branched alkyl group having a carbon number of 1 to10, or an aromatic ring that may have a substituent, R² and R³ arearomatic rings that may be substituted, and X is alkali metal).

(where R¹, R², and R³ independently represent a hydrogen atom, astraight-chain or branched alkyl group having a carbon number of 1 to10, or a straight-chain or branched allyl group having a carbon numberof 1 to 10, and Y is at least one selected from zinc, nickel, cobalt,copper, and chromium).

These materials can suppress the disturbance of an image caused by thecharging action during fixing. Such a feature is attributed to theeffect of the charge polarity of the functional group having an acidvalue of the wax and the metal salt. Moreover, it is possible to preventa decrease in charge amount during continuous use.

The amount of charge control agent added is preferably 0.5 to 5 parts byweight, more preferably 1 to 4 parts by weight, and further preferably 3to 4 parts by weight per 100 parts by weight of the binder resin. Whenit is less than 0.5 parts by weight, the effect of charging action islost. When it is more than 5 parts by weight, color images are prone tohave a dull color.

(5) Pigment

The colorant used in this embodiment may include, e.g., carbon black,iron black, graphite, nigrosine, a metal complex of azo dyes,acetoacetic acid aryl amide monoazo yellow pigments such as C. I.Pigment Yellow 1, 3, 74, 97, and 98, acetoacetic acid aryl amide disazoyellow pigments such as C. I. Pigment Yellow 12, 13, 14, and 17, C. I.Solvent Yellow 19, 77, and 79, or C. I. Disperse Yellow 164. Inparticular, benzimidazolone pigments of C. I. Pigment Yellow 93, 180,and 185 are effective for avoiding filming of the toner on aphotoconductive member.

At least one selected from red pigments such as C. I. Pigment Red 48,49:1, 53:1, 57, 57:1, 81, 122, and 5, red dyes such as C. I. Solvent Red49, 52, 58, and 8, and blue dyes/pigments of phthalocyanine and itsderivative such as C. I. Pigment Blue 15:3 may be added. The addedamount is preferably 3 to 8 parts by weight per 100 parts by weight ofthe binder resin.

The median diameter of the pigment particles is generally not more than1 μm, and preferably 0.01 to 1 μm. When the median diameter is more than1 μm, toner for electrostatic charge image development to be obtained asa final product can have a broader particle size distribution. Moreover,liberated particles are generated and tend to reduce the performance orreliability. When the median diameter is within the above range, thesedisadvantages are eliminated, and the uneven distribution of toner isdecreased. Therefore, the dispersion of the pigment particles in thetoner can be improved, resulting in a smaller variation in performanceand reliability. The median diameter can be measured, e.g., by a laserdiffraction particle size analyzer (LA 920 manufactured by Horiba,Ltd.).

(6) Additive

In this embodiment, the additive may be, e.g., metal oxide fine powdersuch as silica, alumina, titanium oxide, zirconia, magnesia, ferrite,and magnetite, titanate such as barium titanate, calcium titanate, andstrontium titanate, zirconate such as barium zirconate, calciumzirconate, and strontium zirconate, or a mixture of these substances.The additive can be made hydrophobic as needed.

A preferred silicone oil material that is used to treat silica isexpressed by Formula (3).

(where R² is an alkyl group having a carbon number of 1 to 3, R³ is analkyl group having a carbon number of 1 to 3, a halogen modified alkylgroup, a phenyl group, or a substituted phenyl group, R¹ is an alkylgroup having a carbon number of 1 to 3 or an alkoxy group having acarbon number of 1 to 3, and m and n are integers of 1 to 100).

Examples of the silicone oil material include dimethyl silicone oil,methyl hydrogen silicone oil, methyl phenyl silicone oil, cyclicdimethyl silicone oil, epoxy modified silicone oil, carboxyl modifiedsilicone oil, carbinol modified silicone oil, methacrylic modifiedsilicone oil, mercapto modified silicone oil, polyether modifiedsilicone oil, methyl styryl modified silicone oil, alkyl modifiedsilicone oil, fluorine modified silicone oil, amino modified siliconeoil, and chlorophenyl modified silicone oil. The silica that is treatedwith at least one of the above silicone oil materials is usedpreferably. For example, SH200, SH510, SF230, SH203, BY16-823, orBY16-855B manufactured by Toray-Dow Corning Co., Ltd can be used. Thetreatment may be performed by mixing inorganic fine powder with thesilicone oil material using a mixer (e.g., a Henshel mixer). Moreover,the silicone oil material may be spayed onto silica. Alternatively, thesilicone oil material may be dissolved or dispersed in a solvent, andmixed with silica fine powder, followed by removal of the solvent. Theamount of silicone oil material is preferably 1 to 20 parts by weightper 100 parts by weight of the inorganic fine powder.

Examples of a silane coupling agent include dimethyldichlorosilane,trimethylchlorosilane, allyldimethylchlorosilane, hexamethyldisilazane,allylphenyldichlorosilane, benzyl methyl chlorosilane,vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane,vinyltriacetoxysilane, divinylchlorosilane, anddimethylvinylchlorosilane. The silane coupling agent may be treated by adry treatment in which the fine powder is fluidized by agitation or thelike, and an evaporated silane coupling agent is reacted with thefluidized powder, or a wet treatment in which a silane coupling agentdispersed in a solvent is added dropwise to the fine powder.

It is also preferable that the silicone oil material is treated after asilane coupling treatment.

The inorganic fine powder having positive chargeability may be treatedwith aminosilane, amino modified silicone oil expressed by Formula (4),or epoxy modified silicone oil.

(where R¹ and R⁶ are hydrogen, an alkyl group having a carbon number of1 to 3, an alkoxy group, or an aryl group, R² is an alkylene grouphaving a carbon number of 1 to 3 or a phenylene group, R³ is an organicgroup including a nitrogen heterocyclic ring, R⁴ and R⁵ are hydrogen, analkyl group having a carbon number of 1 to 3, or an aryl group, m ispositive numbers of not less than 1, n and q are positive integersincluding 0, and n+1 is positive numbers of not less than 1).

To enhance a hydrophobic treatment, hexamethyldisilazane,dimethyldichlorosilane, or other silicone oil also can be used alongwith the above materials. For example, at least one selected fromdimethyl silicone oil, methylphenyl silicone oil, and alkyl modifiedsilicone oil is preferred to treat the inorganic fine powder.

Fatty acid ester, fatty acid amide, and a fatty acid metal salt also canbe used to treat the surface of the inorganic fine powder, and silica ortitanium oxide fine powder whose surface is treated with at lease one ofthese materials is more preferred.

Examples of the fatty acid and the fatty acid metal salt includecaprylic acid, capric acid, undecylic acid, lauric acid, myristic acid,palmitic acid, stearic acid, behenic acid, montanic acid, lacceric acid,oleic acid, erucic acid, sorbic acid, and linoleic acid. In particular,fatty acid having a carbon number of 15 to 20 is preferred.

Preferred metals of the fatty acid metal salt may be, e.g., aluminum,zinc, calcium, magnesium, lithium, sodium, lead, or barium. Among thesemetals, aluminum, zinc, and sodium are more preferred. Further, mono-and di-fatty acid aluminum such as aluminum distearate(Al(OH)(C₁₇H₃₅COO)₂) or aluminum monostearate (Al(OH)₂(C₁₇H₃₅COO)) areparticularly preferred. By containing a hydroxy group, they can preventovercharge and suppress a transfer failure. Moreover, it is possible toimprove the treatment of the inorganic fine powder such as silica.

The handling property of toner with a small particle size can beimproved, and therefore high image quality and high transfer performancecan be achieved in the development and transfer processes. Thus, anelectrostatic latent image can be developed more faithfully andtransferred without reducing a transfer ratio of the toner particles. Inthe case of tandem transfer, it is also possible to prevent retransferand to suppress transfer voids. Moreover, high image density can beachieved even with a small amount of development. By combining theadditive with a carrier, which will be described later, higherresistance to spent can be obtained, and the handling property of thetoner in a developing unit can be improved, thus increasing theuniformity of the toner concentration. The generation of a developingmemory also can be reduced.

It is preferable that 1.5 to 5.5 parts by weight of the inorganic finepowder having an average particle size of 6 nm to 200 nm is added to 100parts by weight of toner base particles. When the average particle sizeis less than 6 nm, suspended silica particles are generated, and filmingof the toner on a photoconductive member is likely to occur. Therefore,it is difficult to avoid the occurrence of reverse transfer. When theaverage particle size is more than 200 nm, the flowability of the toneris decreased. When the amount of inorganic fine powder added is lessthan 1.5 parts by weight, the flowability of the toner is decreased, andit is difficult to avoid the occurrence of reverse transfer. When it ismore than 5.5 parts by weight, suspended silica particles are generated,and filming of the toner on a photoconductive member is likely to occur,thus degrading the high-temperature offset resistance.

Moreover, it is preferable that 0.5 to 2.5 parts by weight of theinorganic fine powder having an average particle size of 6 nm to 20 nmand 1.0 to 3.5 parts by weight of the inorganic fine powder having anaverage particle size of 30 nm to 200 nm are added to 100 parts byweight of toner base particles. With this configuration, silica can havedifferent functions to ensure larger margins for the handling propertyof the toner in development, reverse transfer, transfer voids, andscattering during transfer. It is also possible to prevent spent on acarrier.

In this case, the ignition loss of the inorganic fine powder having anaverage particle size of 6 nm to 20 nm is preferably 1.5 to 25 wt %, andthe ignition loss of the inorganic fine powder having an averageparticle size of 30 nm to 200 nm is preferably 0.5 to 23 wt %.

By specifying the ignition loss of silica, larger margins can be ensuredagainst reverse transfer, transfer voids, and scattering duringtransfer. When the silica is combined with the carrier or wax, higherresistance to spent can be obtained, and the handling property of thetoner in a developing unit can be improved, thus increasing theuniformity of the toner concentration. The generation of a developingmemory also can be reduced.

When the ignition loss of the inorganic fine powder having an averageparticle size of 6 nm to 20 nm is less than 1.5 wt %, the marginsagainst reverse transfer and transfer voids become narrow. When theignition loss is more than 25 wt %, the surface treatment is notuniform, resulting in charge variations. The ignition loss is preferably1.5 to 20 wt %, and more preferably 5 to 19 wt %.

When the ignition loss of the inorganic fine powder having an averageparticle size of 30 nm to 200 nm is less than 0.5 wt %, the marginsagainst reverse transfer and transfer voids become narrow. When theignition loss is more than 23 wt %, the surface treatment is notuniform, resulting in charge variations. The ignition loss is preferably1.5 to 18 wt %, and more preferably 5 to 16 wt %.

It is also preferable that 0.5 to 1.5 parts by weight of positivelycharged inorganic fine powder having an average particle size of 6 nm to200 nm and an ignition loss of 0.5 to 25 wt % further is added to 100parts by weight of toner base particles.

The addition of the positively charged inorganic fine powder cansuppress the overcharge of the toner for a long period of continuous useand increase the life of a developer. Therefore, the scattering of thetoner during transfer caused by overcharge also can be reduced.Moreover, it is possible to prevent spent on a carrier. When the amountof positively charged inorganic fine powder added is less than 0.5 partsby weight, these effects are not likely to be obtained. When it is morethan 1.5 parts by weight, fog is increased significantly duringdevelopment. The ignition loss is preferably 1.5 to 20 wt %, and morepreferably 5 to 19 wt %.

A drying loss (%) can be determined in the following manner. A containeris dried, allowed to stand and cool, and weighed precisely beforehand.Then, a sample (about 1 g) is put in the container, weighed precisely,and dried for 2 hours with a hot-air dryer at 105° C.±1° C. Aftercooling for 30 minutes in a desiccator, the weight is measured, and thedrying loss is calculated byDrying loss (%)=weight loss (g) by drying/sample amount (g)×100.

An ignition loss can be determined in the following manner. A magneticcrucible is dried, allowed to stand and cool, and weighed preciselybeforehand. Then, a sample (about 1 g) is put in the crucible, weighedprecisely, and ignited for 2 hours in an electric furnace at 500° C.After cooling for 1 hour in a desiccator, the weight is measured, andthe ignition loss is calculated byIgnition loss (%)=weight loss (g) by ignition/sample amount (g)×100.

The amount of moisture absorption of the surfaced-treated inorganic finepowder may be not more than 1 wt %, preferably not more than 0.5 wt %,more preferably not more than 0.1 wt %, and further preferably not morethan 0.05 wt %. When it is more than 1 wt %, the chargeability isdegraded, and filming of the toner on a photoconductive member occurs.The amount of moisture absorption can be measured by using a continuousvapor absorption measuring device (BELSORP 18 manufactured by BEL JAPAN,INC.).

The degree of hydrophobicity can be determined in the following manner.A sample (0.2 g) is weighed in a 250 ml beaker containing 50 ml ofdistilled water. Then, methanol is added from a buret, whose end is putinto the water, until the whole inorganic fine powder is wet whilecontinuing the stirring slowly with a magnetic stirrer. Based on theamount a (ml) of methanol required to wet the inorganic fine powdercompletely, the degree of hydrophobicity is calculated byDegree of hydrophobicity (%)=(a/(50+a))×100.(7) Powder physical Characteristics of Toner

In this embodiment, the volume-average particle size of toner baseparticles including a binder resin, a colorant, and wax is 3 to 7 μm,preferably 3 to 6.5 μm, and more preferably 3 to 4.5 μm. The particlesize distribution is such that the content of the toner base particleshaving a particle size of 2.52 to 4 μm in a number distribution is 5 to65% by number, and the toner base particles having a particle size of6.35 to 10.1 μm in a volume distribution is 5 to 35% by volume.Preferably, the particle size distribution is such that the content ofthe toner base particles having a particle size of 2.52 to 4 μm in thenumber distribution is 15 to 65% by number, and the toner base particleshaving a particle size of 6.35 to 10.1 μm in the volume distribution is5 to 25% by volume. More preferably, the particle size distribution issuch that the content of the toner base particles having a particle sizeof 2.52 to 4 μm in the number distribution is 25 to 65% by number, andthe toner base particles having a particle size of 6.35 to 10.1 μm inthe volume distribution is 5 to 15% by volume. The toner base particleswith the above characteristics can provide high-resolution imagequality, prevent reverse transfer and transfer voids during tandemtransfer, and achieve the oilless fixing. When the volume-averageparticle size is more than 7 μm, the image quality and the transferproperty cannot be ensured together. When the volume-average particlesize is less than 3 μm, the handling property of the toner particles indevelopment is reduced. When the content of the toner base particleshaving a particle size of 2.52 to 4 μm in the number distribution isless than 5% by number, the image quality and the transfer propertycannot be ensured together. When it is more than 65% by number, thehandling property of the toner particles in development is reduced. Whenthe toner base particles having a particle size of 6.35 to 10.1 μm inthe volume distribution is more than 35% by volume, the image qualityand the transfer property cannot be ensured together. When it is lessthan 5% by volume, the toner productivity is reduced and the cost isincreased. The coefficient of variation in the volume particle sizedistribution of the toner base particles is preferably 15 to 32%, morepreferably 15 to 30%, and further preferably 15 to 25%. The coefficientof variation in the number particle size distribution of the toner baseparticles is preferably 15 to 35%, more preferably 15 to 30%, andfurther preferably 15 to 25%.

The coefficient of variation is obtained by dividing a standarddeviation by an average particle size of the toner particles based onthe measurement using Coulter Counter (manufactured by CoulterElectronics, Inc.). When the particle sizes of n particles are measured,the standard deviation can be expressed by the square root of the valuethat is obtained by dividing the square of a difference between each ofthe n measured values and the mean value by (n−1). In other words, thecoefficient of variation indicates the degree of expansion of theparticle size distribution. When the coefficient of variation of thevolume particle size distribution or the number particle sizedistribution is less than 15%, the production becomes difficult, and thecost is increased. When the coefficient of variation of the volumeparticle size distribution is more than 32%, or when the coefficient ofvariation of the number particle size distribution is more than 35%, theparticle size distribution is broader, and the agglomeration of toner isstronger. This may lead to filming of the toner on a photoconductivemember, a transfer failure, and difficulty of recycling the residualtoner in a cleanerless process. The fine powder in toner affects theflowability, image quality, and storage stability of the toner, filmingof the toner on a photoconductive member, developing roller, or transfermember, the aging property, the transfer property, and particularly themultilayer transfer property in a tandem system. The fine powder alsoaffects the offset resistance, glossiness, and transmittance in theoilless fixing. When the toner includes a release agent such as wax toachieve the oilless fixing, the amount of fine powder may affectcompatibility between the oilless fixing and the tandem transferproperty. If the amount of fine powder is excessively large, i.e., thecontent of the toner base particles having a particle size of 2.52 to 4μm is more than 65% by number, the wax is not dispersed completely andis likely to be exposed on the toner surface, resulting in filming ofthe toner on a photoconductive member, developing roller, or transfermember. The adhesion of the fine powder to a heat roller is large, andthus tends to cause offset. In the tandem system, the agglomeration ofthe toner is likely to be stronger, which easily leads to a transferfailure of the second color during multilayer transfer. If the amount offine powder is reduced, the image quality may be degraded. Therefore, anappropriate range is necessary. The particle size distribution ismeasured, e.g., by using Coulter Counter TA-II (manufactured by CoulterElectronics, Inc.). An interface (manufactured by Nikkaki Bios Co.,Ltd.) for outputting a number distribution and a volume distribution anda personal computer are connected to the Coulter Counter TA-II. Anelectrolytic solution (about 50 ml) is prepared by including asurface-active agent (sodium lauryl sulfate) so as to have aconcentration of 1%. About 2 mg of measuring toner is added to theelectrolytic solution. This electrolytic solution in which the sample issuspended is dispersed for about 3 minutes with an ultrasonic dispersingdevice, and then is measured using the 70 μm aperture of the CoulterCounter TA-II. In the 70 μm aperture system, the measurement range ofthe particle size distribution is 1.26 μm to 50.8 μm. However, theregion smaller than 2.0 μm is not suitable for practical use because themeasurement accuracy or reproducibility is low under the influence ofexternal noise or the like. Therefore, the measurement range is set from2.0 μm to 50.8 μm.

A compression ratio calculated from a static bulk density and a dynamicbulk density can be used as an index of the flowability of toner. Thetoner flowability may be affected by the particle size distribution andparticle shape of the toner, the additive, and the type or amount ofwax. When the particle size distribution of the toner is narrow, lessfine powder is present, the toner surface is not rough, the toner shapeis close to spherical, a large amount of additive is added, and theadditive has a small particle size, the compression ratio is reduced,and the toner flowability is increased. The compression ratio ispreferably 5 to 40%, and more preferably 10 to 30%. This can ensurecompatibility between the oilless fixing and the multilayer transferproperty in the tandem system. When the compression ratio is less than5%, the fixability is degraded, and particularly the transmittance islikely to be lower. Moreover, toner scatting from the developing rollermay be increased. When the compression ratio is more than 40%, thetransfer property is decreased to cause a transfer failure such astransfer voids in the tandem system.

(8) Carrier

A resin-coated carrier of this embodiment preferably includes a carriercore provided with a coating of fluorine modified silicone resincontaining an aminosilane coupling agent. The carrier core may be, e.g.,an iron powder carrier core, a ferrite carrier core, a magnetite carriercore, or a resin-dispersed carrier core in which a magnetic body isdispersed in the resin. An example of the ferrite carrier core isexpressed generally by(MO)_(X)(Fe₂O₃)_(Y)where M includes at least one selected from Cu, Zn, Fe, Mg, Mn, Ca, Li,Ti, Ni, Sn, Sr, Al, Ba, Co, and Mo, and X and Y are a molar ratio andsatisfy X+Y=100. The ferrite carrier core includes Fe₂O₃ as the mainmaterial and at least one oxide of M selected from Cu, Zn, Fe, Mg, Mn,Ca, Li, Ti, Ni, Sn, Sr, Al, Ba, Co, and Mo. The ferrite carrier core maybe produced in the following manner. First, the above materials such aseach oxide are blended in an appropriate amount. The blend is placed ina wet ball mill, and then is pulverized and mixed for 10 hours. Theresultant mixture is dried and kept at 950° C. for 4 hours. Moreover,the mixture is pulverized for 24 hours in the wet ball mill, to which abinder (polyvinyl alcohol), an antifoaming agent, a surface-activeagent, and the like are added, thus forming a slurry with a particlesize of 5 μm or less. The slurry is granulated and dried. The granulatedsubstance is kept at 1300° C. for 6 hours while controlling the oxygenconcentration. Subsequently, this substance was pulverized and furtherclassified to achieve a desired particle size distribution.

A fluorine modified silicone resin may be used for the resin coating ofthe present invention. The fluorine modified silicone resin ispreferably a cross-linked fluorine modified silicone resin obtained bythe reaction between an organosilicon compound containing aperfluoroalkyl group and polyorganosiloxane. It is preferable that 3 to20 parts by weight of the organosilicon compound containing aperfluoroalkyl gourp is mixed with 100 parts by weight of thepolyorganosiloxane. The polyorganosiloxane preferably has at lease onerepeating unit selected from Formulas (5) and (6).

(where R¹ and R² are a hydrogen atom, a halogen atom, a hydroxy group, amethoxy group, an alkyl group having a carbon number of 1 to 4, or aphenyl group, R³ and R⁴ are an alkyl group having a carbon number of 1to 4 or a phenyl group, and m represents a mean degree of polymerizationand is positive integers (preferably in the range of 2 to 500, and morepreferably in the range of 5 to 200)).

(where R¹ and R² are a hydrogen atom, a halogen atom, a hydroxy group, amethoxy group, an alkyl group having a carbon number of 1 to 4, or aphenyl group, R³, R⁴, R⁵, and R⁶ are an alkyl group having a carbonnumber of 1 to 4 or a phenyl group, and n represents a mean degree ofpolymerization and is positive integers (preferably in the range of 2 to500, and more preferably in the range of 5 to 200)).

Examples of the organosilicon compound containing a perfluoroalkyl groupinclude CF₃CH₂CH₂Si(OCH₃)₃, C₄F₉CH₂CH₂Si(CH₃)(OCH₃)₂,C₈F₁₇CH₂CH₂Si(OCH₃)₃, C₈F₁₇CH₂CH₂Si(OC₂H₅)₃, and(CF₃)₂CF(CF₂)₈CH₂CH₂Si(OCH₃)₃. In particular, a compound containing atrifluoropropyl group is preferred.

In this embodiment, the aminosilane coupling agent is included in theresin coating. As the aminosilane coupling agent, e.g., the followingknown materials can be used:γ-(2-aminoethyl)aminopropyltrimethoxysilane,γ-(2-aminoethyl)aminopropylmethyldimethoxysilane, and octadecylmethyl[3-(trimethoxysilyl)propyl]ammonium chloride (corresponding to SH6020,SZ6023, and AY43-021 manufactured by Toray-Dow Corning Co., Ltd.);KBM602, KBM603, KBE903, and KBM573 (manufactured by Shin-Etsu ChemicalCo., Ltd.). In particular, the primary amine is preferred. The secondaryor tertiary amine that is substituted with a methyl group, an ethylgroup, or a phenyl group has weak polarity and is less effective forraising the charge property of toner. When the amino group is replacedby an aminomethyl group, an aminoethyl group, or an aminophenyl group,the end of the silane coupling agent can be the primary amine. However,the amino group in the straight-chain organic group extended from silanedoes not contribute to the charge raising property and is affected bymoisture under high humidity. Therefore, although the carrier may havecharging ability for initial toner because the amino group is at theend, the charging ability is decreased during operation, resulting in ashort life of the carrier.

By using the above aminosilane coupling agent with the fluorine modifiedsilicone resin of this embodiment, the toner can be charged negativelywhile maintaining a sharp charge distribution. When the toner issupplied, it shows a quick rise in charge, and thus the tonerconsumption can be reduced. Moreover, the aminosilane coupling agent hasthe effect comparable to that of a cross-linking agent. Therefore, itcan increase the degree of cross-linking of the coating of fluorinemodified silicone resin as a base resin. Further, the hardness of theresin coating is improved, so that abrasion or peeling can be reducedover a long period of use. Accordingly, higher resistance to spent canbe obtained, and the electrification can be stabilized by suppressing adecrease in the charging ability of the carrier, thus improvingdurability.

When wax having a low melting point is added to toner with the aboveconfiguration in an amount greater than a given value, the chargeabilityof the toner is rather unstable because the toner surface consistsmainly of resin. There may be some cases where the chargeability isweaker and the rise in charge is slower. This tends to cause fog, pooruniformity of a solid image, and transfer voids or skipping duringtransfer. However, combining the toner with the carrier of thisembodiment can overcome these problems and improve the handling propertyof the toner in a developing unit. Thus, the uniformity in density of animage can be improved in both the start and end of the development.Moreover, a so-called developing memory, i.e., a history that is leftafter taking a solid image, can be reduced.

The ratio of the aminosilane coupling agent to the resin is 5 to 40 wt%, and preferably 10 to 30 wt %. When the ratio is less than 5 wt %, noeffect of the aminosilane coupling agent is observed. When the ratio ismore than 40 wt %, the degree of cross-linking of the resin coating isexcessively high, and a charge-up phenomenon is likely to occur. Thismay lead to image defects such as underdevelopment.

The resin coating also may include conductive fine powder to stabilizeelectrification and to prevent charge-up. Examples of the conductivefine powder include carbon black such as oil furnace black or acetyleneblack, a semiconductive oxide such as titanium oxide or zinc oxide, andpowder of titanium oxide, zinc oxide, barium sulfate, aluminum borate,or potassium titanate coated with tin oxide, carbon black, or metal. Thespecific resistance is preferably not more than 10¹⁰Ω·cm. The content ofthe conductive fine powder is preferably 1 to 15 wt %. When theconductive fine powder is included to some extent in the resin coating,the hardness of the resin coating can be improved by a filler effect.However, when the content is more than 15 wt %, the conductive finepowder may interfere with the formation of the resin coating, resultingin lower adherence and hardness. An excessive amount of conductive finepowder in a full color developer may cause the color contamination oftoner that is transferred and fixed on paper.

The carrier used in the present invention preferably has an averageparticle size of 20 to 70 μm. When the average particle size is lessthan 20 μm, the abundance ratio of fine particles in the carrierparticle distribution is increased, and magnetization per carrierparticle is reduced. Therefore, the carrier is likely to be developed ona photoconductive member. When the average particle size is more than 70μm, the specific surface area of the carrier particles is smaller, andthe toner retaining ability is decreased to cause toner scattering. Forfull color images including many solid portions, the reproduction of thesolid portions is particularly worse.

A method for forming a coating on the carrier core is not particularlylimited, and any known coating methods can be used, such as a dippingmethod of dipping core material powder in a solution for forming acoating layer, a spaying method of spaying a solution for forming acoating layer on the surface of a core material, a fluidized bed methodof spraying a solution for forming a coating layer to a core materialwhile the core material is floated by fluidizing air, and a kneader andcoater method of mixing a core material and a solution for forming acoating layer in a kneader and coater, and removing a solvent. Inaddition to these wet coating methods, a dry coating method also can beused. The dry coating method includes, e.g., mixing resin powder and acore material at high speed, and fusing the resin powder on the surfaceof the core material by utilizing the frictional heat. In particular,the wet coating method is preferred for coating of the fluorine modifiedsilicone resin containing an aminosilane coupling agent of the presentinvention.

A solvent of the solution for forming a coating layer is notparticularly limited as long as it dissolves the coating resin, and canbe selected in accordance with the coating resin to be used. Examples ofthe solvent include aromatic hydrocarbons such as toluene and xylene,ketones such as acetone and methyl ethyl ketone, and ethers such astetrahydrofuran and dioxane. The amount of coating resin is preferably0.2 to 6.0 wt %, more preferably 0.5 to 5.0 wt %, further preferably 0.6to 4.0 wt %, and most preferably 0.7 to 3 wt % with respect to thecarrier core. When the amount of coating resin is less than 0.2 wt %, auniform coating cannot be formed on the carrier surface. Therefore, thecarrier is affected significantly by the characteristics of the carriercore and cannot provide a sufficient effect of the fluorine modifiedsilicone resin containing an aminosilane coupling agent. When the amountof coating resin is more than 6.0 wt %, the coating is too thick, andgranulation between the carrier particles occurs. Therefore, the carrierparticles are not likely to be uniform.

It is preferable that a baking treatment is performed after coating thecarrier core with the fluorine modified silicone resin containing anaminosilane coupling agent. A means for the baking treatment is notparticularly limited, and either of external and internal heatingsystems may be used. For example, a fixed or fluidized electric furnace,a rotary kiln electric furnace, or a burner furnace can be used as well.Alternatively, baking may be performed with a microwave. The bakingtemperature should be high enough to provide the effect of fluorinesilicone that can improve the spent resistance of the resin coating,e.g., preferably 200° C. to 350° C., and more preferably 220° C. to 280°C. The treatment time is preferably 1.5 to 2.5 hours. A lowertemperature may degrade the hardness of the resin coating itself, whilean excessively high temperature may cause a charge reduction.

(9) Two-component Development

Both direct-current bias and alternating-current bias are appliedbetween a photoconductive member and a developing roller. In this case,it is preferable that the frequency is 1 to 10 kHz, thealternating-current bias is 1.0 to 2.5 kV (p-p), and the circumferentialvelocity ratio of the photoconductive member to the developing roller is1:1.2 to 1:2. More preferably, the frequency is 3.5 to 8 kHz, thealternating-current bias is 1.2 to 2.0 kV (p-p), and the circumferentialvelocity ratio of the photoconductive member to the developing roller is1:1.5 to 1:1.8.

Further preferably, the frequency is 5.5 to 7 kHz, thealternating-current bias is 1.5 to 2.0 kV (p-p), and the circumferentialvelocity ratio of the photoconductive member to the developing roller is1:1.6 to 1:1.8.

When the above development process configuration is used with toner or atwo-component developer of this embodiment, it is possible to reproducedots faithfully, to improve the development γ characteristics, and toensure a high quality image and the oilless fixability. Moreover,charge-up can be suppressed under low humidity even with a highresistance carrier. Therefore, high image density can be obtained duringcontinuous use. By combining toner that can exhibit high chargeability,the carrier configuration, and the alternating-current bias, theadhesion between the toner and the carrier can be reduced, and the imagedensity can be maintained. Moreover, it is possible to reduce fog and toreproduce dots faithfully. When the frequency is less than 1 kHz, thedot reproducibility is decreased, resulting in poor reproduction ofmiddle tones. When the frequency is more than 10 kHz, the toner cannotfollow in the development region, and no effect is observed. In thetwo-component development using a high resistance carrier, the frequencywithin the above range is more effective for reciprocating actionbetween the carrier and the toner than between the developing roller andthe photoconductive member. Thus, the toner can be liberated slightlyfrom the carrier. This may improve the dot reproducibility and themiddle tone reproducibility, and provide high image density. When thealternating-current bias is lower than 1.0 kV (p-p), the effect ofsuppressing charge-up cannot be obtained. When the alternating-currentbias is more than 2.5 kV (p-p), fog is increased. When thecircumferential velocity ratio is less than 1:1.2 (the developing rollergets slower), it is difficult to ensure the image density. When thecircumferential velocity ratio is more than 1:2 (the developing rollergets faster), toner scatting is increased.

(10) Tandem Color Process p This embodiment employs the followingtransfer process for high-speed color image formation. A plurality oftoner image forming stations, each of which includes a photoconductivemember, a charging member, and a toner support member, are used. In aprimary transfer process, an electrostatic latent image formed on thephotoconductive member is made visible by development, and a toner imagethus developed is transferred to an endless transfer member that is incontact with the photoconductive member. The primary transfer process isperformed continuously in sequence so that a multilayer toner image isformed on the transfer member. Then, a secondary transfer process isperformed by collectively transferring the multilayer toner image fromthe transfer member to a transfer medium such as paper or OHP sheet. Thetransfer process satisfies the relationship expressed byd1/v≦0.65where d1 (mm) is a distance between the first primary transfer positionand the second primary transfer position, and v (mm/s) is acircumferential velocity of the photoconductive member. Thisconfiguration can reduce the machine size and improve the printingspeed. To process 16 sheets (A4) per minute and to make the size smallenough to be used for SOHO (small office/home office) purposes, adistance between the toner image forming stations should be as short aspossible, while the processing speed should be enhanced. Thus, d1/v≦0.65is considered as the minimum requirement to achieve both small size andhigh printing speed.

In this configuration, however, when a period of time from the primarytransfer of the first color (yellow toner) to that of the second color(magenta toner) is extremely short, the charge of the transfer member orthe charge of the transferred toner hardly is relieved. Therefore, whenthe magenta toner is transferred onto the yellow toner, it is repelledby the charging action of the yellow toner. This may lead to lowertransfer efficiency and transfer voids. When the third color (cyan)toner is transferred onto the yellow and the magenta toner, the cyantoner is scattered, and a transfer failure or transfer voids is causedconsiderably. Moreover, toner having a specified particle size isdeveloped selectively with repeated use, and the individual tonerparticles differ significantly in flowability, so that frictional chargeopportunities are different. Thus, the charge amount is varied tofurther reduce the transfer property. In such a case, therefore, thetoner or two-component developer of this embodiment can stabilize thecharge distribution and suppress the overcharge and flowabilityvariations of toner. Accordingly, it is possible to prevent lowertransfer efficiency, transfer voids, and reverse transfer withoutsacrificing the fixing property.

(11) Cleanerless Process

The toner of this embodiment can be used preferably in an electrographicapparatus that employs a cleanerless process as a basic configuration.While a cleaning process recycles the toner remaining on thephotoconductive member after a transfer process, the cleanerless processperforms the subsequent charging, exposure, and development processeswithout the cleaning process.

The use of the toner or two-component developer of this embodiment cansuppress the agglomeration of the toner, prevent overcharge, stabilizeelectrification, and achieve high transfer efficiency. Moreover, theresidual toner in the non-image portion can be recycled successfully fordevelopment because of the improved uniform dispersibility in the resin,good chargeability, and the releasability of materials. Thus, there isno developing memory in which the previous image pattern has been leftin the non-image portion.

(11) Oiless Color Fixing

The toner of this embodiment can be used preferably in an electrographicapparatus having a fixing process with an oilless fixing configurationthat applies no oil to any fixing means. As a heating means,electromagnetic induction heating is suitable in view of reducing awarm-up time and power consumption. The oilless fixing configurationincludes a magnetic field generation means and a heating and pressingmeans. The heating and pressing means includes at least a rotationalheating member and a rotational pressing member. There is a certain nipbetween the rotational heating member and the rotational pressingmember. The rotational heating member includes at least a heatgeneration layer formed by electromagnetic induction and a releaselayer. A transfer medium such as copy paper to which toner has beentransferred is allowed to pass between the rotational heating member andthe rotational pressing member so as to fix the toner.

Another configuration in which a heating member is separated from afixing member and a fixing belt runs between the two members also may beused preferably. The fixing belt may be, e.g., a nickel electroformedbelt having heat resistance and deformability or a heat-resistantpolyimide belt. Silicone rubber, fluorocarbon rubber, or fluorocarbonresin may be used as a surface coating to improve the releasability.

In the conventional fixing process, release oil has been applied toprevent offset. The toner that exhibits releasability without using oilcan eliminate the need for application of the release oil. However, ifthe release oil is not applied to the fixing means, it can be chargedeasily. Therefore, when an unfixed toner image is close to the heatingmember or the fixing member, the toner may be scattered due to theinfluence of charge. Such scattering is likely to occur particularlyunder low temperature and low humidity.

In contrast, the toner of this embodiment can prevent the occurrence ofoffset without using oil and also can provide high color transmittance.Thus, the use of the toner of this embodiment can suppress overcharge aswell as scattering caused by the charging action of the heating memberor the fixing member.

The toner or two-component developer of the present invention also canbe used in the following image forming apparatuses.

(i) An image forming apparatus includes a developing means that appliesa direct-current bias and an alternating-current bias having a frequencyof 1 to 10 kHz and a bias of 1.0 to 2.5 kV (p-p) between aphotoconductive member and a developing roller. The circumferentialvelocity ratio of the photoconductive member to the developing roller is1:1.2 to 1:2. This image forming apparatus uses toner includingaggregated particles that include at least resin particles, pigmentparticles, and wax particles. The wax is at least one selected from A:ester wax that has an iodine value of not more than 25, a saponificationvalue of 30 to 300, and an endothermic peak temperature (melting point)of 50° C. to 100° C. based on the DSC method, and B: wax that isobtained by the reaction of alkyl alcohol having a carbon number of 4 to30, unsaturated polycarboxylic acid or its anhydride, and unsaturatedhydrocarbon wax and has an acid value of 1 to 80 mgKOH/g and anendothermic peak temperature (melting point) of 50° C. to 120° C. basedon the DSC method.

(ii) An image forming apparatus includes a developing means that appliesa direct-current bias and an alternating-current bias having a frequencyof 1 to 10 kHz and a bias of 1.0 to 2.5 kV (p-p) between aphotoconductive member and a developing roller. The circumferentialvelocity ratio of the photoconductive member to the developing roller is1:1.2 to 1:2. This image forming apparatus uses a two-componentdeveloper including toner and a carrier. The toner includes aggregatedparticles that include at least resin particles, pigment particles, andwax particles. A fused film of the resin is formed on the surface of thetoner. The wax is at least one selected from A: ester wax that has aniodine value of not more than 25, a saponification value of 30 to 300,and an endothermic peak temperature (melting point) of 50° C. to 100° C.based on the DSC method, and B: wax that is obtained by the reaction ofalkyl alcohol having a carbon number of 4 to 30, unsaturatedpolycarboxylic acid or its anhydride, and unsaturated hydrocarbon waxand has an acid value of 1 to 80 mgKOH/g and an endothermic peaktemperature (melting point) of 50° C. to 120° C. based on the DSCmethod. The carrier includes magnetic particles as a core material, andat least the surface of the core material is coated with a fluorinemodified silicone resin containing an aminosilane coupling agent.

(iii) An image forming apparatus includes a plurality of toner imageforming stations, each of which includes an image support member, acharging member for forming an electrostatic latent image on the imagesupport member, and toner support member. The electrostatic latent imageformed on each of the image support members is made visible bydevelopment with toner including aggregated particles that include atleast resin particles, pigment particles, and wax particles. The wax isat least one selected from A: ester wax that has an iodine value of notmore than 25, a saponification value of 30 to 300, and an endothermicpeak temperature (melting point) of 50° C. to 100° C. based on the DSCmethod, and B: wax that is obtained by the reaction of alkyl alcoholhaving a carbon number of 4 to 30, unsaturated polycarboxylic acid orits anhydride, and unsaturated hydrocarbon wax and has an acid value of1 to 80 mgKOH/g and an endothermic peak temperature (melting point) of50° C. to 120° C. based on the DSC method. This image forming apparatushas a transfer system in which the toner images obtained by thedevelopment of the electrostatic latent images are transferredsuccessively to a transfer medium. The transfer system satisfies therelationship expressed by d1/v≦0.65 (sec) where d1 (mm) is a distancebetween a first transfer position and a second transfer position, orbetween the second transfer position and a third transfer position, orbetween the third transfer position and a fourth transfer position, andv (mm/s) is a circumferential velocity of the image support member.

(iv) An image forming apparatus includes a plurality of toner imageforming stations, each of which includes an image support member, acharging member for forming an electrostatic latent image on the imagesupport member, and toner support member. The electrostatic latent imageformed on each of the image support members is made visible bydevelopment with a two-component developer including toner and acarrier. The toner includes aggregated particles that include at leastresin particles, pigment particles, and wax particles. A fused film ofthe resin is formed on the surface of the toner. The wax is at least oneselected from A: ester wax that has an iodine value of not more than 25,a saponification value of 30 to 300, and an endothermic peak temperature(melting point) of 50° C. to 100° C. based on the DSC method, and B: waxthat is obtained by the reaction of alkyl alcohol having a carbon numberof 4 to 30, unsaturated polycarboxylic acid or its anhydride, andunsaturated hydrocarbon wax and has an acid value of 1 to 80 mgKOH/g andan endothermic peak temperature (melting point) of 50° C. to 120° C.based on the DSC method. The carrier includes magnetic particles as acore material, and at least the surface of the core material is coatedwith a fluorine modified silicone resin containing an aminosilanecoupling agent. This image forming apparatus has a transfer system inwhich the toner images obtained by the development of the electrostaticlatent images are transferred successively to a transfer medium. Thetransfer system satisfies the relationship expressed by d1/v≦0.65 (sec)where d1 (mm) is a distance between a first transfer position and asecond transfer position, or between the second transfer position and athird transfer position, or between the third transfer position and afourth transfer position, and v (mm/s) is a circumferential velocity ofthe image support member.

In this embodiment, ester wax or wax derived from unsaturatedhydrocarbon wax is used. The polarity of a surface-active agent of thewax particle dispersion is opposite to that of a surface-active agent ofthe resin particle dispersion. When aggregated particles are formed, asurface-active agent having the same polarity as that of thesurface-active agent of the wax particle dispersion is added. Therefore,it is possible to reduce the amount of wax or pigment particles that arenot aggregated and thus are suspended in the aqueous medium, to achieveuniform mixing and aggregation, and to improve the colorreproducibility. Moreover, the two-component developer includes acarrier in which the carrier core is coated with the fluorine modifiedsilicone resin containing an aminosilane coupling agent. Thisconfiguration can achieve the oilless fixing that prevents offsetwithout using oil while maintaining high OHP transmittance, andeliminate spent of the toner components on the carrier to make the lifelonger. Moreover, high transfer efficiency can be ensured by suppressingtransfer voids or scattering during transfer.

Next, an example of the manufacturing process of toner of the presentinvention will be described by referring to FIG. 5. Reference numeral 20is an emulsion polymerization tank in which monomers, an anionicsurface-active agent (emulsifier), a polymerization initiator,ion-exchanged water, and the like are supplied from a raw materialsupply line 21, and emulsion polymerization is performed. The resultantpolymer is resin particles with an average particle size of 0.1 to 0.2μm. Reference numeral 30 is a pigment dispersion tank in which apigment, an anionic surface-active agent, and ion-exchanged water aresupplied from a raw material supply line 31 to produce pigment particleswith an average particle size of 0.1 to 0.2 μm. Reference numeral 40 isa wax dispersion tank (see FIGS. 3 and 4) in which wax, a cationicsurface-active agent, and ion-exchanged water are supplied from a rawmaterial supply line 44 to produce wax particles with an averageparticle size of 0.2 to 0.5 μm. When the primary particles are producedin each of the tanks 20, 30, and 40, valves 22, 32, and 49 are opened tolet the primary materials and a cationic surface-active agent (at apredetermined mixing ratio) into an aggregation tank 50 through supplylines 51, 52, and 53, respectively. Then, aggregated particles(secondary particles) are formed by ionic aggregation of the aboveparticles in water. In this case, it is important to incorporate waxinto the aggregated particles efficiently. Thereafter, the aggregatedparticles are coated with a fused film by heating. Next, a valve 54 isopened to let the aggregated particles into a filtration separation tank60 through a supply line 61. In the filtration separation tank 60, theaggregated particles are separated. Then, a valve 62 is opened to letthe aggregated particles into a washing tank 70 through a supply line71. After the aggregated particles are washed with water, a valve 72 isopened to let them into the filtration separation tank 60 through asupply line 73, thereby separating the aggregated particles from water.This operation is repeated several times, and then a valve 63 is openedto provide toner of the purified aggregated particles. Subsequently, thetoner is dried to make a toner product.

In the above manufacturing process, a funnel glass filter No. 5A (7 μm)may be used as a filter of the filtration separation tank 60.

FIG. 6A is a transmission electron microscope (TEM) image of tonerparticles of a toner base M3 produced in the following example(magnification: 15000×). All the resins are melted and do not remain inthe form of particles. In FIG. 6A, the central portion of each particleseems white because the wax is incorporated into the resin. The resinand pigment particles are dispersed around the central portion as anintermediate layer. Moreover, a resin layer (outermost shell) is formedaround the intermediate layer.

FIG. 6B is a TEM image of toner particles of a toner base M6 produced inthe following example (magnification: 12000×). All the resins are meltedand do not remain in the form of particles. In FIG. 6B, the waxparticles, the pigment particles, and the resin are mixed and dispersedin each particle, and the outer layer of the particle is a resin layer.Compared to FIG. 6A, there are few particles in which only wax ispresent in the central portion. This can be attributed to the influenceof a difference in the heat characteristics or composition of the wax.The volume average particle size of the toner is 3 μm to 7 μm.

Hereinafter, the present invention will be described in more detail byway of examples. However, the present invention is not limited to theexamples.

Carrier Producing Example 1

MnO (39.7 mol %), MgO (9.9 mol %), Fe₂O₃ (49.6 mol %), and SrO (0.8 mol%) were placed in a wet ball mill, and then were pulverized and mixedfor 10 hours. The resultant mixture was dried, kept at 950° C. for 4hours, and temporarily fired. This was pulverized for 24 hours in a wetball mill, and then was granulated and dried by a spray dryer. Thegranulated substance was kept in an electric furnace at 1270° C. for 6hours in an atmosphere of oxygen concentration of 2%, and fully fired.The fired substance was ground and further classified, thus producing acore material of ferrite particles that had an average particle size of50 μm and a saturation magnetization of 65 emu/g in an applied magneticfield of 3000 oersted.

Next, 250 g of polyorganosiloxane expressed by Formula 7 in which(CH₃)₂SiO— unit is 15.4 mol % and Formula 8 in which CH₃SiO_(3/2)— unitis 84.6 mol % was allowed to react with 21 g of CF₃CH₂CH₂Si(OCH₃)₃ toproduce a fluorine modified silicone resin. This reaction was ademethoxy reaction with which an organosilicon compound containing aperfluoroalkyl group was introduced into polyorganosiloxane. Then, 100 gof the fluorine modified silicone resin (as represented in terms ofsolid content) and 10 g of aminosilane coupling agent(γ-aminopropyltriethoxysilane) were weighed and dissolved in 300 ml oftoluene solvent.

(where R¹, R², R³, and R⁴ are a methyl group, and m is a mean degree ofpolymerization of 100)

(where R¹, R², R³, R⁴, R⁵, and R⁶ are a methyl group, and n is a meandegree of polymerization of 80)

Using a dip and dry coater, 10 kg of the ferrite particles were coatedby stirring the resin coating solution for 20 minutes, and then werebaked at 260° C. for 1 hour, providing a carrier A1.

Carrier Producing Example 2

A core material was produced in the same manner as the Carrier ProducingExample 1 except that CF₃CH₂CH₂Si(OCH₃)₃ was changed toC₈F₁₇CH₂CH₂Si(OCH₃)₃, and a coating was applied, thus providing acarrier A2.

Carrier Producing Example 3

A core material was produced in the same manner as the Carrier ProducingExample 1 except that a conductive carbon (manufactured by KetjenblackInternational Corporation EC) was dispersed in an amount of 5 wt % perthe resin solid content by using a pearl mill, and a coating wasapplied, thus providing a carrier A3.

Carrier Producing Example 4

A core material was produced in the same manner as the Carrier ProducingExample 3 except that the amount of aminosilane coupling agent to beadded was changed to 30 g, and a coating was applied, thus providing acarrier A4.

Carrier Producing Comparative Example 5

A core material was produced in the same manner as the Carrier ProducingExample 3 except that the amount of aminosilane coupling agent to beadded was changed to 50 g, and a coating was applied, thus providing acarrier b1.

Carrier Producing Comparative Example 6

As a coating resin, 100 g of straight silicone (SR-2411 manufactured byDow Corning Toray Silicone Co., Ltd.) was weighed in terms of solidcontent and dissolved in 300 cc of toluene solvent. Using a dip and drycoater, 10 kg of the ferrite particles were coated by stirring the resincoating solution for 20 minutes, and then were baked at 210° C. for 1hour, providing a carrier b2.

Carrier Producing Comparative Example 7

As a coating resin, 100 g of perfluorooctylethyl acrylate/methacrylatecopolymer was weighed in terms of solid content and dissolved in 300 ccof toluene solvent. Using a dip and dry coater, 10 kg of the ferriteparticles were coated by stirring the resin coating solution for 20minutes, and then were baked at 200° C. for 1 hour, providing a carrierb3.

Carrier Producing Comparative Example 8

As a coating resin, 100 g of acrylic modified silicone resin (KR-9706manufactured by Shin-Etsu Chemical Co., Ltd.) was weighed in terms ofsolid content and dissolved in 300 cc of toluene solvent. Using a dipand dry coater, 10 kg of the ferrite particles were coated by stirringthe resin coating solution for 20 minutes, and then were baked at 210°C. for 1 hour, providing a carrier b4.

Examples of the toner of the present invention will be described below.However, the present invention is not limited to the examples. In thefollowing examples, Mn is a number-average molecular weight, Mw is aweight-average molecular weight, Mz is a Z average molecular weight, Tmis a softening point, and Tg is a glass transition point.

(1) Resin Particle Dispersion R1

A monomer solution including 192 g of styrene, 48 g of n-butylacrylate,and 3.6 g of acrylic acid was dispersed in 200 ml of ion-exchanged waterwith 6 g of anionic surface-active agent (NEOGEN RK manufactured byDai-Ichi Kogyo Seiyaku Co., Ltd.), 12 g of dodecanethiol, and 2.4 g ofcarbon tetrabromide. Then, 2.4 g of potassium persulfate was added tothe resultant solution, and emulsion polymerization was performed at 70°C. for 6 hours. Thus, a resin particle dispersion R1 was prepared, inwhich the resin particles having Mn of 3100, Mw of 25000, Tm of 115° C.,Tg of 52° C., and a median diameter of 0.12 μm were dispersed.

(2) Resin Particle Dispersion R2

A monomer solution including 176 g of styrene, 64 g of n-butylacrylate,and 3.6 g of acrylic acid was dispersed in 200 ml of ion-exchanged waterwith 6 g of anionic surface-active agent (NEOGEN RK manufactured byDai-Ichi Kogyo Seiyaku Co., Ltd.), 12 g of dodecanethiol, and 2.4 g ofcarbon tetrabromide. Then, 2.4 g of potassium persulfate was added tothe resultant solution, and emulsion polymerization was performed at 70°C. for 5 hours. Thus, a resin particle dispersion R2 was prepared, inwhich the resin particles having Mn of 3000, Mw of 22000, Tm of 108° C.,Tg of 50° C., and a median diameter of 0.18 μm were dispersed.

(3) Resin Particle Dispersion R3

A monomer solution including 212 g of styrene, 28 g of n-butylacrylate,and 3 g of acrylic acid was dispersed in 200 ml of ion-exchanged waterwith 6 g of anionic surface-active agent (NEOGEN RK manufactured byDai-Ichi Kogyo Seiyaku Co., Ltd.), 12 g of dodecanethiol, and 2.4 g ofcarbon tetrabromide. Then, 2.4 g of potassium persulfate was added tothe resultant solution, and emulsion polymerization was performed at 70°C. for 5 hours. Thus, a resin particle dispersion R3 was prepared, inwhich the resin particles having Mn of 2800, Mw of 23000, Tm of 103° C.,Tg of 62° C., and a median diameter of 0.21 μm were dispersed.

(4) Colorant Particle Dispersion

20 g of magenta pigment (KETRED307 manufactured by Dainippon Ink andChemicals, Inc.), 3 g of anionic surface-active agent (NEOGEN Rmanufactured by Dai-Ichi Kogyo Seiyaku Co., Ltd), and 77 ml ofion-exchanged water were mixed and dispersed by using an ultrasonicdispersing device at an oscillation frequency of 30 kHz for 20 minutes.Thus, a colorant particle dispersion was prepared, in which the colorantparticles having a median diameter of 0.12 μm were dispersed.

(5) Wax Particle Dispersion

30 g of wax in Table 1, 2 or 3, 2 g of stearic acid amine hydrochloride,0.5 g of polyvinyl alcohol, and 68 ml of ion-exchanged water were mixedand heated at a temperature that was not less than the melting point ofthe wax. Using a dispersing device as shown in FIGS. 3 and 4, themixture was dispersed at a rotational speed of 40 m/s or more for 3minutes. Thus, a wax particle dispersion was prepared, in which the waxparticles having a medium diameter of 0.1 to 0.2 μm were dispersed. WA-4was heated under high pressure to produce a dispersion.

TABLE 1 Melting Volume Heating Saponi- point ratio loss Iodine ficationWax Material Tw(° C.) Ct(%) Ck(wt %) value value WA-1 Hydrogenatedjojoba oil 68 18.5 2.8 2 95.7 WA-2 Carnauba wax 83 15.3 4.1 10 80 WA-3Hydrogenated meadowfoam oil 71 3 2.5 2 90

TABLE 2 Melting Acid value Pene- point (mgKOH/ tration Tw(° C.) g)number WA-4 polypropylene/maleic 98 45 1 anhydride/alcohol-type wax witha carbon number of less than 30/tert-butylperoxy isopropylmonocarbonate: 100/20/8/4 parts by weight

TABLE 3 Mnr Mwr Mzr Mwr/Mnr Mzr/Mnr Peak WA-1 1009 1072 1118 1.06 1.111.02 × 10³ WA-2 1100 1198 1290 1.09 1.17  1.2 × 10³ WA-3 1015 1078 11241.06 1.11 1.03 × 10³ WA-4 1400 2030 2810 1.45 2.01  2.1 × 10³(6) Preparation of Toner Base M1 (The Mixing and Aggregation of aDispersion and the Production of Heat-treated Particles)

In a 2000 ml four-neck flask equipped with a cooling tube and athermometer were placed 210 g of first resin particle dispersion R1, 20g of colorant particle dispersion, 50 g of wax particle dispersion WA-1,and 200 ml of ion-exchanged water, and then mixed and dispersed by usinga homogenizer (Ultratalax T50 manufactured by IKA CO., LTD.). Thus, aparticle dispersion was prepared.

Subsequently, 2.8 g of cationic surface-active agent (SANISOL B-50manufactured by Kao Corporation) and 60 g of ion-exchanged water wereadded to the particle dispersion. The flask was put in an oil bath,heated to 50° C. while stirring the dispersion, and maintained for 60minutes, thus providing an aggregated particle dispersion. Theaggregated particle dispersion was observed by using a Coulter counter(Multisizer 2 manufactured by Coulter Electronics, Inc.) and confirmedto include particles having a volume-average particle size of about 4.1μm. Thereafter, the temperature of the aggregated particle dispersionwas raised to 55° C. and kept for 1 hour, thus providing a meltedparticle dispersion that included melted particles having avolume-average particle size of about 4.8 μm.

The pH of the melted particle dispersion was adjusted to 7.0 by dropping0.5 M/L NaOH. The stainless steel flask was sealed with a magnetic seal,heated to 90° C. while stirring the dispersion, and maintained for 2hours. After cooling, the reaction product (toner base particles) wasfiltered and washed three times with ion-exchanged water. The toner baseparticles thus obtained were dried at 40° C. for 6 hours by using afluid-type dryer, resulting in a toner base M1.

(7) Preparation of Toner Base M2

A toner base M2 was produced in the same manner as the toner base M1except that the resin particle dispersion R3 and 70 g of wax particledispersion WA-4 were used in preparing an aggregated particledispersion. (8) Preparation of toner base M3

In a stainless steel round flask were placed 210 g of first resinparticle dispersion R1, 20 g of colorant particle dispersion, 50 g ofwax particle dispersion WA-1, and 110 parts by weight of ion-exchangedwater, and then mixed and dispersed by using a homogenizer (UltratalaxT50 manufactured by IKA CO., LTD.). Thus, a particle dispersion wasprepared.

Subsequently, 2.8 g of cationic surface-active agent (SANISOL B-50manufactured by Kao Corporation) and 60 g of ion-exchanged water wereadded to the particle dispersion. The flask was put in an oil bath,heated to 50° C. while stirring the dispersion, and maintained for 60minutes, thus providing an aggregated particle dispersion. Theaggregated particle dispersion was observed by using a Coulter counter(Multisizer 2 manufactured by Coulter Electronics, Inc.) and confirmedto include particles having a volume-average particle size of about 4.1μm. Thereafter, the temperature of the aggregated particle dispersionwas raised to 55° C. and kept for 1 hour, thus providing a meltedparticle dispersion that included melted particles having avolume-average particle size of about 4.8 μm.

The pH of the melted particle dispersion was adjusted to 7.0 by dropping0.5 M/L NaOH. Then, 44 g of second resin particle dispersion R1 wasadded to the melted particle dispersion. The stainless steel flask wassealed with a magnetic seal, heated to 90° C. while stirring thedispersion, and maintained for 2 hours. Consequently, the second resinparticles were formed into a fused film, and a toner base particledispersion was provided. After cooling, the toner base particles werefiltered and washed three times with ion-exchanged water. The toner baseparticles thus obtained were dried at 40° C. for 6 hours by using afluid-type dryer, resulting in a toner base M3 in which the second resinserved as a shell.

(9) Preparation of Toner Base M4

A toner base M4 was produced in the same manner as the toner base M3except that the first resin particle dispersion R1 and 65 g of waxparticle dispersion WA-2 were used in preparing an aggregated particledispersion, and the second resin particle dispersion R3 was added afterpH adjustment.

(10) Preparation of Toner Base M5

A toner base M5 was produced in the same manner as the toner base M3except that the first resin particle dispersion R2 and 75 g of waxparticle dispersion WA-3 were used in preparing an aggregated particledispersion, and the second resin particle dispersion R3 was added afterpH adjustment.

(11) Preparation of Toner Base M6

A toner base M6 was produced in the same manner as the toner base M3except that the first resin particle dispersion R2 and 85 g of waxparticle dispersion WA-4 were used in preparing an aggregated particledispersion, and the second resin particle dispersion R3 was added afterpH adjustment.

Cyan toner, yellow toner, and black toner were produced in the samemanner as magenta toner. Phthalocyanine pigments (KETBLUE111manufactured by Dainippon Ink and Chemicals, Inc.) were used for thecyan toner, yellow pigments (Y180 manufactured by Clariant) were usedfor the yellow toner, and carbon black (MA100S manufactured byMitsubishi Chemical Corporation) was used for the black toner.

(12) Preparation of Toner Base m11

A toner base m11 was produced in the same manner as the toner base M1except that the first resin particle dispersion R2 and 85 g of paraffinwax (mp 80° C.) instead of the wax particle dispersion were used inpreparing an aggregated particle dispersion.

The toner thus obtained caused lower transfer efficiency, transfervoids, and filming on a photoconductive member that was attributed tothe dispersion of the wax. When the durability of the developer was 10k, fog was increased. For fixing, the transmittance was 50% or less. Thetoner coagulated in a storage life test.

(13) Preparation of Toner Base m12

A toner base m12 was produced in the same manner as the toner base M1except that the first resin particle dispersion R2 and 85 g ofpolypropylene wax (mp 145° C.) instead of the wax particle dispersionwere used in preparing an aggregated particle dispersion.

The toner thus obtained caused lower transfer efficiency, transfervoids, and filming on a photoconductive member that was attributed tothe dispersion of the wax. When the durability of the developer was near5 k, the amount of charge was decreased, and fog was increased. Forfixing, the transmittance was 50% or less.

(14) Preparation of Toner Base m13

A toner base m13 was produced in the same manner as the toner base M1except that a cationic surface-active agent was not added to theparticle dispersion including the resin particles, the colorantparticles, and the wax particles. In this case, however, the aggregatedparticles were not formed stably, and the particle size distributionbecame broader. Moreover, many wax and pigment particles were notaggregated and suspended in the aqueous medium. The residual wax wasattached to the toner base.

(15) Preparation of Toner Base m14

A toner base m14 was produced in the same manner as the toner base M3except that a cationic surface-active agent was not added to theparticle dispersion including the resin particles, the colorantparticles, and the wax particles. In this case, however, the aggregatedparticles were not formed stably, and the particle size distributionbecame broader. Moreover, many wax and pigment particles were notaggregated and suspended in the aqueous medium. Further, a uniform shellwas not provided due to agglomeration of the second resin particles.

Table 4 shows the additives used in this example. The amount of chargewas measured by a blow-off method using frictional charge with anuncoated ferrite carrier. Under the environmental conditions of 25° C.and 45% RH, 50 g of carrier and 0.1 g of silica or the like were mixedin a 100 ml polyethylene container, and then stirred by verticalrotation at a speed of 100 min⁻¹ for 5 minutes and 30 minutes,respectively. Thereafter, 0.3 g of sample was taken for each stirringtime, and a nitrogen gas was blown on the samples at 1.96×10⁴ (Pa) for 1minute.

It is preferable that the 5-minute value is −100 to −800 μC/g and the30-minute value is −50 to −600 μC/g for the negative chargeability.Silica having a high charge amount can function well in a smallquantity.

TABLE 4 Inorganic Particle Methanol Moisture Ignition Drying 5-min/ finesize titration absorption loss loss 5-min 30-min 30-min powder Material(nm) (%) (wt %) (wt %) (wt %) value value value S1 Silica treated withdimethyl 6 88 0.1 24 0.2 −890 −740 83.15 silicone oil S2 Silica treatedwith 16 88 0.1 8.5 0.2 −720 −520 72.22 dimethylpolysiloxane S3 Silicatreated with dimethyl 16 88 0.12 9.5 0.2 −685 −511 74.60 siliconeoil/aluminum distearate S4 Silica treated with dimethyl 40 89 0.10 6.80.2 −710 −580 81.69 silicone oil S5 Titanium oxide treated with 120 890.10 8.9 0.2 −370 −175 47.30 trimethylmethoxysilane/zinc stearate S6Silica treated with amino 40 73 0.10 12.5 0.2 280 150 53.57 modifiedsilicone oil S7 Silica treated with amino 120 73 0.10 8.8 0.2 410 32078.05 modified silicone oil

Table 5 shows the toner material compositions used in this example.

TABLE 5 Toner Toner base Additive A Additive B TM1 M1 S1(1.2) TM2 M2S2(1.8) S4(0.5) TM3 M3 S3(1.5) TM4 M4 S1(1.0) S5(1.5) TM5 M5 S2(1.5)S6(0.3) TM6 M6 S3(1.5) S7(0.5) TM7 M1 S1(1.2) S7(0.5) TM8 M3 S2(1.8)S6(0.3) TM9 M4 S3(1.5) S5(1.5) TC1 m11 S1(1.2) TC2 m12 S1(1.2) TC3 m13S1(1.2) TC4 m14 S1(1.2)

The number in the parentheses is the amount (parts by weight) of theadditive added per 100 parts by weight of the toner base. The externaladdition treatment was performed by using FM20B with a Z0S0-type mixerblade, an input amount of 1 kg, a number of revolutions of 2000 min⁻¹,and a treating time of 5 minutes.

FIG. 1 is a cross-sectional view showing the configuration of a fullcolor image forming apparatus used in this example. In FIG. 1, the outerhousing of a color electrophotographic printer is not shown.

A transfer belt unit 17 includes a transfer belt 12, a first color(yellow) transfer roller 10Y, a second color (magenta) transfer roller10M, a third color (cyan) transfer roller 10C, a fourth color (black)transfer roller 10K, a driving roller 11 made of aluminum, a secondtransfer roller 14 made of an elastic body, a second transfer followerroller 13, a belt cleaner blade 16 for cleaning a toner image thatremains on the transfer belt 12, and a roller 15 located opposite to thebelt cleaner blade 16. The first to fourth color transfer rollers 10Y,10M, 10C, and 10K are made of an elastic body.

A distance between the first color (Y) transfer position and the secondcolor (M) transfer position is 35 mm (which is the same as a distancebetween the second color (M) transfer position and the third color (C)transfer position and a distance between the third color (C) transferposition and the fourth color (K) transfer position). Thecircumferential velocity of a photoconductive member is 125 mm/s.

The transfer belt 12 can be obtained by kneading a conductive filler inan insulating resin and making a film with an extruder. In this example,polycarbonate resin (e.g., European Z300 manufactured by Mitsubishi GasKagaku Co., Ltd.) was used as the insulating resin, and 5 parts byweight of conductive carbon (e.g., “KETJENBLACK”) were added to 95 partsby weight of the polycarbonate resin to form a film. The surface of thefilm was coated with a fluorocarbon resin. The film had a thickness ofabout 100 μm, a volume resistance of 10⁷ to 10¹²Ω·cm, and a surfaceresistance of 10⁷ to 10¹²Ω/sq. The use of this film can improve the dotreproducibility and prevent slackening of the transfer belt 12 over along period of use or charge accumulation effectively. By coating thefilm surface with a fluorocarbon resin, the filming of toner on thesurface of the transfer belt 12 caused by a long period of use also canbe suppressed effectively. When the volume resistance is less than10⁷Ω·cm, retransfer is likely to occur. When the volume resistance ismore than 10¹²Ω·cm, the transfer efficiency is degraded.

A first transfer roller 10 is a urethane foam roller of conductivecarbon and has an outer diameter of 10 mm. The resistance value is 10²to 10⁶Ω. In the first transfer operation, the first transfer roller 10is pressed against a photoconductive member 1 with a force of about 1.0to 9.8 (N) via the transfer belt 12, so that toner is transferred fromthe photoconductive member 1 to the transfer belt 12. When theresistance value is less than 10²Ω, reverse transfer is likely to occur.When the resistance value is more than 10⁶Ω, a transfer failure islikely to occur. The force less than 1.0 (N) may cause a transferfailure, and the force more than 9.8 (N) may cause transfer voids.

The second transfer roller 14 is a urethane foam roller of conductivecarbon and has an outer diameter of 15 mm. The resistance value is 10²to 10⁶Ω. The second transfer roller 14 is pressed against the followerroller 13 via the transfer belt 12 and a transfer medium 19 such as apaper or OHP sheet. The follower roller 13 is rotated in accordance withthe movement of the transfer belt 12. In the second transfer operation,the second transfer roller 14 is pressed against the follower roller 13with a force of 5.0 to 21.8 (N), so that toner is transferred from thetransfer belt 12 to the transfer medium 19. When the resistance value isless than 10²Ω, reverse transfer is likely to occur. When the resistancevalue is more than 10⁶Ω, a transfer failure is likely to occur. Theforce less than 5.0 (N) may cause a transfer failure, and the force morethan 21.8 (N) may increase the load and generate jitter easily.

Four image forming units 18Y, 18M, 18C, and 18K for yellow (Y), 1.

The image forming units 18Y, 18M, 18C, and 18K have the same componentsexcept for a developer contained therein. For simplification, only theimage forming unit 18Y for yellow (Y) will be described, and anexplanation of the other units will not be repeated.

The image forming unit is configured as follows. Reference numeral 1 isa photoconductive member, 3 is pixel laser signal light, and 4 is adeveloping roller of aluminum that has an outer diameter of 12 mm andincludes a magnet with a magnetic force of 1200 gauss. The developingroller 4 is located opposite to the photoconductive member 1 with a gapof 0.3 mm between them, and rotates in the direction of the arrow. Astirring roller 6 stirs toner and a carrier in a developing unit andsupplies the toner to the developing roller 4. The mixing ratio of thetoner to the carrier is read from a permeability sensor (not shown), andthe toner is supplied timely from a toner hopper (not shown). A magneticblade 5 is made of metal and controls a magnetic brush layer of adeveloper on the developing roller 4. In this example, 150 g ofdeveloper was introduced, and the gap was 0.4 mm. Although a powersupply is not shown in FIG. 1, a direct voltage of −500 V and analternating voltage of 1.5 kV (p-p) at 6 kHz were applied to thedeveloping roller 4. The circumferential velocity ratio of thephotoconductive member 1 to the developing roller 4 was 1:1.6. Themixing ratio of the toner to the carrier was 93:7. The amount ofdeveloper in the developing unit was 150 g.

A charging roller 2 is made of epichlorohydrin rubber and has an outerdiameter of 12 mm. A direct-current bias of −1.2 kV is applied to thecharging roller 2 for charging the surface of the photoconductive member1 to −600 V. Reference numeral 8 is a cleaner, 9 is a waste toner box,and 7 is a developer.

A paper is conveyed from the lower side of the transfer belt unit 17,and a paper conveying path is formed so that a paper 19 is transportedby a paper feed roller (not shown) to a nip portion where the transferbelt 12 and the second transfer roller 14 are pressed against eachother.

Toner on the transfer belt 12 is transferred to the paper 19 by +1000 Vapplied to the second transfer roller 14, and then is conveyed to afixing portion in which the toner is fixed. The fixing portion includesa fixing roller 201, a pressure roller 202, a fixing belt 203, a heatroller 204, and an induction heater 205.

FIG. 2 shows a fixing process. A belt 203 runs between the fixing roller201 and the heat roller 204. A predetermined load is applied between thefixing roller 201 and the pressure roller 202 so that a nip is formedbetween the belt 203 and the pressure roller 202. The induction heater205 including a ferrite core 206 and a coil 207 is provided on theperiphery of the heat roller 204, and a temperature sensor 208 isarranged on the outer surface. The belt 203 is formed by arranging a Nisubstrate (30 μm), silicone rubber (150 μm), and PFA(tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) (30 μm) inlayers. The pressure roller 202 is pressed against the fixing roller 201by a spring 209. A recording material 19 with toner 210 is moved along aguide plate 211. The fixing roller 201 (fixing member) includes a hollowcore 213, an elastic layer 214 formed on the hollow core 213, and asilicone rubber layer 215 formed on the elastic layer 214. The hollowcore 213 is made of aluminum and has a length of 250 mm, an outerdiameter of 14 mm, and a thickness of 1 mm. The elastic layer 214 ismade of silicone rubber with a rubber hardness (JIS-A) of 20 degreesbased on the JIS standard and has a thickness of 3 mm. The siliconerubber layer 215 has a thickness of 3 mm. Therefore, the outer diameterof the fixing roller 201 is about 20 mm. The fixing roller 201 isrotated at 125 mm/s by receiving a driving force from a driving motor(not shown).

The heat roller 204 includes a hollow pipe having a thickness of 1 mmand an outer diameter of 20 mm. The surface temperature of the fixingbelt is controlled to 170° C. by using a thermistor.

The pressure roller 202 (pressure member) has a length of 250 mm and anouter diameter of 20 mm, and includes a hollow core 216 and an elasticlayer 217 formed on the hollow core 216. The hollow core 216 is made ofaluminum and has an outer diameter of 16 mm and a thickness of 1 mm. Theelastic layer 217 is made of silicone rubber with a rubber hardness(JIS-A) of 55 degrees based on the JIS standard and has a thickness of 2mm. The pressure roller 202 is mounted rotatably, and a 5.0 mm width nipis formed between the pressure roller 202 and the fixing roller 201under a one-sided load of 147N given by the spring 209.

The operations will be described below. In the full color mode, all thefirst transfer rollers 10 of Y, M, C, and K are lifted and pressedagainst the respective photoconductive members 1 of the image formingunits via the transfer belt 12. At this time, a direct-current bias of+800 V is applied to each of the first transfer rollers 10. An imagesignal is transmitted through the laser beam 3 and enters thephotoconductive member 1 whose surface has been charged by the chargingroller 2, thus forming an electrostatic latent image. The electrostaticlatent image formed on the photoconductive member 1 is made visible bytoner on the developing roller 4 that is rotated in contact with thephotoconductive member 1.

In this case, the image formation rate (125 mm/s, which is equal to thecircumferential velocity of the photoconductive member) of the imageforming unit 18Y is set so that the speed of the photoconductive memberis 0.5 to 1.5% slower than the traveling speed of the transfer belt 12.

In the image forming process, signal light 3Y is input to the imageforming unit 18Y, and an image is formed with Y toner. At the same timeas the image formation, the Y toner image is transferred from thephotoconductive member 1Y to the transfer belt 12 by the action of thefirst transfer roller 10Y, to which a direct voltage of +800 V isapplied.

There is a time lag between the first transfer of the first color (Y)and the first transfer of the second color (M). Then, signal light 3M isinput to the image forming unit 18M, and an image is formed with Mtoner. At the same time as the image formation, the M toner image istransferred from the photoconductive member 1M to the transfer belt 12by the action of the first transfer roller 10M. In this case, the Mtoner is transferred onto the first color (Y) toner that has been formedon the transfer belt 12. Subsequently, the C toner and K toner imagesare formed in the same manner and transferred by the action of the firsttransfer rollers 10C and 10K. Thus, YMCK toner images are formed on thetransfer belt 12. This is a so-called tandem process.

A color image is formed on the transfer belt 12 by superimposing thefour color toner images in registration. After the last transfer of theK toner image, the four color toner images are transferred collectivelyto the paper 19 fed by a feeding cassette (not shown) at matched timingby the action of the second transfer roller 14. In this case, thefollower roller 13 is grounded, and a direct voltage of +1 kV is appliedto the second transfer roller 14. The toner images transferred to thepaper 19 are fixed by a pair of fixing rollers 201 and 202. Then, thepaper 19 is ejected through a pair of ejecting rollers (not shown) tothe outside of the apparatus. The toner that is not transferred andremains on the transfer belt 12 is cleaned by the belt cleaner blade 16to prepare for the next image formation.

Table 6 shows the results of visual images formed by theelectrophotographic apparatus in FIG. 1. In this case, a transferfailure in the character portion of a full color image with three colorsof toner and the winding of a paper around the fixing belt wereevaluated. The amount of charge was measured by a blow-off method usingfrictional charge with a ferrite carrier. Under the environmentalconditions of 25° C. and 45% RH, 0.3 g of sample was taken to evaluatethe durability, and a nitrogen gas was blown on the sample at 1.96×10⁴(Pa) for 1 minute. The acceptable level of the image density was 1.3 ormore. The evaluations of fog, uniformity of a solid image, transferskipping in letters, reverse transfer, and transfer voids wererepresented by ∘ (good), Δ (somewhat worse), and X (unsuitable forpractical use).

TABLE 6 Image Filming on density (ID) Uniformity Transferphotoconductive initial/after of solid skipping in Reverse TransferDeveloper Toner Carrier member test Fog image letters transfer voidsDM11 TM1 A1 Not occur 1.49/1.52 ◯ ◯ ◯ ◯ ◯ cm1 TM2 b1 Not occur 1.34/1.28◯ Δ ◯ Δ Δ DM12 TM3 A2 Not occur 1.47/1.51 ◯ ◯ ◯ ◯ ◯ DM13 TM4 A3 Notoccur 1.52/1.53 ◯ ◯ ◯ ◯ ◯ DM14 TM5 A4 Not occur 1.34/1.32 ◯ ◯ ◯ ◯ ◯ cm2TM6 b2 Not occur 1.38/1.23 ◯ Δ ◯ Δ Δ cm3 TM7 b3 Not occur 1.41/1.29 ◯ Δ◯ Δ Δ DM15 TM8 A1 Not occur 1.44/1.47 ◯ ◯ ◯ ◯ ◯ DM16 TM9 A2 Not occur1.49/1.45 ◯ ◯ ◯ ◯ ◯ DM17 TM3 A3 Not occur 1.48/1.45 ◯ ◯ ◯ ◯ ◯ DM18 TM4A4 Not occur 1.41/1.39 ◯ ◯ ◯ ◯ ◯ cm4 tm11 A1 Occur 1.37/1.32 Δ Δ X X Xcm5 tm12 A2 Occur 1.48/1.39 Δ Δ X X X cm6 tm13 A3 Occur 1.48/1.42 Δ Δ XX X cm7 tm14 A4 Occur 1.34/1.29 Δ Δ X X X cm8 tm11 b1 Occur 1.21/1.02 XX X X X cm9 tm12 b2 Occur 1.46/1.25 X X X X X cm10 tm13 b3 Occur1.23/0.97 X X X X X cm11 tm14 b4 Occur 1.48/1.23 X X X X X

When visual images were formed by using the developers DM11 to DM18,there was no disturbance in horizontal lines, no scattering toner, andno transfer void. The black solid images were uniform, and images withsignificantly high resolution and high quality were reproduced even at16 lines per mm. Moreover, high-density images having an image densityof not less than 1.3 were obtained. When a white image was taken aftersuccessively printing 10 copies of the solid image, no background fogwas present in the non-image portions.

Subsequently, when a solid image was taken, a supply or mixing failureof the toner and the carrier did not occur, and a developing memory wasnot generated.

In the long period durability test after 300,000 copies of A4 paper, theflowability and the image density were not changed very much, and thecharacteristics were stable. There was almost no spent of the tonercomponents on the carrier. A change in carrier resistance was reduced, adecrease in charge amount was suppressed, and no fog was caused. Theamount of charge hardly varied under high temperature and high humidityconditions as well as low temperature and low humidity conditions.

The transfer voids were not a problem for practical use, and reversetransfer occurred to a lesser extent. The transfer efficiency was about95%. In the case of a full color image formed by superimposing threecolors, a transfer failure and reverse transfer did not occur.

The filming of the toner on the photoconductive member or the transferbelt was not a problem for practical use. Moreover, a cleaning failureof the photoconductive member or the transfer belt did not occur.

Even with a full color image, there was almost no disturbance orscattering of the toner during fixing, and a paper was not wound aroundthe fixing belt.

When the developers cm1 to cm3 were used at a process speed of 100 mm/swhile the photoconductive members were spaced 70 mm apart, the transfervoids, skipping in letters during transfer, and reverse transfer wereacceptable levels. However, when the process speed was increased to 120mm/s or the distance between the photoconductive members was 60 mm,transfer voids and reverse transfer occurred, and the characteristicswere degraded. The solid image uniformity also was somewhat reduced(indicated by Δ).

For the developers cm4 to cm11, transfer voids and reverse transfer wereincreased, and a cleaning failure of the photoconductive member or thetransfer belt was caused. The filming of the toner on thephotoconductive member and fog also occurred considerably.

Moreover, spent of the toner on the carrier was increased, and thecarrier resistance was changed significantly. Further, the amount ofcharge was decreased, and fog was likely to be larger. Under hightemperature and high humidity conditions, fog was increased due to areduction in charge amount. Under low temperature and low humidityconditions, the image density was reduced due to an increase in chargeamount. The transfer efficiency was decreased to about 60% to 70%. Whena solid image was taken for development, the image got blurred withrepeated operation. The wax adhered to the developing blade, and unusualimages with vertical strips were formed during continuous use. Inoutputting an image of three superimposed colors, a paper was woundaround the fixing belt. The toner scattered during fixing.

Next, an offset resistance test was conducted in the following manner. Asolid image was fixed on an OHP sheet in an amount of 1.2 g/cm² or moreat a process speed of 100 mm/s by using a fixing device provided with anoilless belt. Table 7 shows the results. The toner of TM 1 to TM6 didnot cause paper jam in the nip portion. When a green solid image wasfixed on a plain paper, no offset occurred until 122,000 copies. Even ifa silicone or fluorine-based fixing belt was used without oil, thesurface of the belt did not wear. The transmittance and the offsetresistance at high temperatures were evaluated. In this case, theprocess speed was 100 mm/s, and the fixing temperature was 180° C. Thetransmittance was measured with 700 nm light by using aspectrophotometer (U-3200 manufactured by Hitachi, Ltd.). Theevaluations of fixability, offset resistance, and storage stability wereshown in Table 7.

TABLE 7 OHP trans- High-temperature Winding Toner mittance offsetgeneration Storage around disturbance (%) (° C.) test fixing belt duringfixing TM1 92.5 220 ◯ Not occur None TM2 93.5 230 ◯ Not occur None TM391.8 230 ◯ Not occur None TM4 90.1 230 ◯ Not occur None TM5 87.8 220 ◯Not occur None TM6 87.8 230 ◯ Not occur None tm11 48.2 170 X OccurScattering tm12 47.8 160 X Occur Scattering tm13 75.8 180 X OccurScattering tm14 68.4 170 X Occur Scattering

As shown in Table 7, the OHP transmittance of TM1 to TM6 was 80% ormore. TM1 to TM6 also had a high offset temperature of 220° C. or moreand exhibited favorable fixability when the fixing roller was usedwithout oil. Moreover, agglomeration hardly was observed under thestorage conditions of 60° C. for 5 hours. For the toner of tm11 to tm14,however, agglomeration was observed in the storage test, and thetemperature range of offset resistance was narrow.

1. A method for producing toner comprising: (i) forming aggregatedparticles in an aqueous medium by mixing and aggregating (a) a firstresin particle dispersion in which first resin particles are dispersedin a surface-active agent, (b) a colorant particle dispersion in whichcolorant particles are dispersed in a surface-active agent having thesame polarity as that of the surface-active agent for the first resinparticle dispersion, (c1) a wax particle dispersion in which at leastester wax that has an iodine value of not more than 25, a saponificationvalue of 30 to 300, and an endothermic peak temperature (melting point)of 50° C. to 100° C. based on a DSC method is dispersed in asurface-active agent having the opposite polarity to that of thesurface-active agent for the first resin particle dispersion, or (c2) awax particle dispersion in which at least wax that is obtained by areaction of alkyl alcohol having a carbon number of 4 to 30, unsaturatedpolycarboxylic acid or its anhydride, and unsaturated hydrocarbon waxand has an acid value of 1 to 80 mgKOH/g and an endothermic peaktemperature (melting point) of 50° C. to 120° C. based on the DSC methodis dispersed in a surface-active agent having the opposite polarity tothat of the surface-active agent for the first resin particledispersion, and (d) a surface-active agent having the same polarity asthat of the surface-active agent for the wax particle dispersion that isadded to the aqueous medium in addition to the surface-active agent inthe wax particle dispersion, (ii) forming melted particles by heatingthe aggregated particles for a predetermined time in the aqueous medium;(iii) mixing the melted particles with a second resin particledispersion in which second resin particles are dispersed in asurface-active agent (e) so that the second resin particles adhere tothe melted particles; and (iv) forming fused films of the second resinparticles on surfaces of the melted particles by heating.
 2. The methodaccording to claim 1, wherein in a molecular weight distribution of theester wax based on gel permeation chromatography (GPC), a number-averagemolecular weight is 100 to 5000, a weight-average molecular weight is200 to 10000, a ratio (weight-average molecular weight/number-averagemolecular weight) of the weight-average molecular weight to thenumber-average molecular weight is 1.01 to 8, a ratio (Z averagemolecular weight/number-average molecular weight) of the Z averagemolecular weight to the number-average molecular weight is 1.02 to 10,and there is at least one molecular weight maximum peak in a range of5×10² to 1×10⁴, and the ester wax has a heating loss of not more than 8wt % at 220° C.
 3. The method according to claim 1, wherein the meltedparticle dispersion has a pH of 7 to 10, and the second resin particlesare mixed with and adhere to the melted particles by adding an inorganicmetal salt.
 4. The method according to claim 3, wherein the particlesare separated from the water by filtration.
 5. The method according toclaim 1, wherein an additive is added further to the surface of thetoner and the additive is silica whose surface is treated with at leastone selected from the group consisting of fatty acid ester, fatty acidantide, and a fatty acid metal salt.
 6. The method according to claim 5,wherein an additive is added further to the surface of the toner, and asthe additive, 0.5 to 2.5 parts by weight of inorganic fine powder havingan average particle size of 6 nm to 20 nm and an ignition loss of 1.5 to25 wt %, and 1.0 to 3.5 parts by weight of inorganic fine powder havingan average particle size of 30 nm 200 nm and an ignition loss of 0.5 to23 wt % are added to 100 parts by weight of toner base particles.
 7. Themethod according to claim 1, wherein an additive is added further to thesurface of the toner, and as the additive, 0.5 to 2.5 parts by weight ofinorganic fine powder having an average particle size of 6 nm to 20 nmand an ignition loss of 1.5 to 25 wt %, 1.0 to 3.5 parts by weight ofinorganic fine powder having an average particle size oF 30 nm to 200 nmand an ignition loss of 0.5 to 23 wt %, and 0.5 to 1.5 parts by weightof positively charged inorganic fine powder having an average particlesize of 6 nm 200 nm and an ignition loss of 0.5 to 25 wt % are added to100 parts by weight of toner base particles.
 8. The method according toclaim 1, wherein lauryl amine hydrochloride or stearic acid aminehydrochloride is used as a surface-active agent for the wax particledispersion.
 9. The method according to claim 1, wherein polyvinylalcohol or water-soluble cellulose is used with lauryl aminehydrochloride or stearic acid amine hydrochloride as a surface-activeagent for the wax particle dispersion.
 10. The method according to claim1, wherein the wax in the wax particle dispersion (c2) has aweight-average molecular weight of 1000 to 6000, a Z average molecularweight of 1500 to 9000, a ratio (weight-average molecularweight/number-average molecular weight) of the weight-average molecularweight to the number-average molecular weight of 1.1 to 3.8, a ratio (Zaverage molecular weight/number-average molecular weight) of the Zaverage molecular weight to the number-average molecular weight of 1.5to 6.5, and at least one molecular weight maximum peak in a rangeofi1×10³ to 3 ×10⁴.